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 $210.75   12.339%   $236.7544   $236.75   $236.75   $236.80  
  Purchase #2 $226.48   11.266%   $251.9952   $252.00   $252.00   $252.00  
  Purchase #3 $226.32   9.324%   $247.4221   $247.42   $247.40   $247.40  
  Purchase #4 $157.66   7.310%   $169.1849   $169.18   $169.20   $169.20  
  Purchase #5 $32.39   6.801%   $34.5928   $34.59   $34.60   $34.60  
  Purchase #6 $203.48   11.537%   $226.9555   $226.96   $226.95   $227.00  
  Purchase #7 $233.38   12.372%   $262.2538   $262.25   $262.25   $262.30  
  7 purchase totals = $1,290.46       $1,429.1587   $1,429.15   $1,429.15   $1,429.30