Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $213.49   5.870%   $226.0219   $226.02   $226.00   $226.00  
  Purchase #2 $210.55   11.691%   $235.1654   $235.17   $235.15   $235.20  
  Purchase #3 $165.48   7.495%   $177.8827   $177.88   $177.90   $177.90  
  Purchase #4 $239.90   3.692%   $248.7571   $248.76   $248.75   $248.80  
  Purchase #5 $205.81   9.443%   $225.2446   $225.24   $225.25   $225.20  
  Purchase #6 $119.74   11.588%   $133.6155   $133.62   $133.60   $133.60  
  Purchase #7 $219.56   12.672%   $247.3826   $247.38   $247.40   $247.40  
  7 purchase totals = $1,374.53       $1,494.0698   $1,494.07   $1,494.05   $1,494.10