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 $64.58   6.277%   $68.6337   $68.63   $68.65   $68.60  
  Purchase #2 $231.66   11.781%   $258.9519   $258.95   $258.95   $259.00  
  Purchase #3 $208.93   3.808%   $216.8861   $216.89   $216.90   $216.90  
  Purchase #4 $246.65   7.721%   $265.6938   $265.69   $265.70   $265.70  
  Purchase #5 $8.50   9.727%   $9.3268   $9.33   $9.35   $9.30  
  Purchase #6 $183.33   10.443%   $202.4752   $202.48   $202.50   $202.50  
  Purchase #7 $130.34   4.200%   $135.8143   $135.81   $135.80   $135.80  
  7 purchase totals = $1,073.99       $1,157.7818   $1,157.78   $1,157.85   $1,157.80