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 $103.92   11.691%   $116.0693   $116.07   $116.05   $116.10  
  Purchase #2 $190.75   4.126%   $198.6203   $198.62   $198.60   $198.60  
  Purchase #3 $21.28   5.672%   $22.487   $22.49   $22.50   $22.50  
  Purchase #4 $91.82   11.331%   $102.2241   $102.22   $102.20   $102.20  
  Purchase #5 $67.49   11.412%   $75.192   $75.19   $75.20   $75.20  
  Purchase #6 $236.76   7.860%   $255.3693   $255.37   $255.35   $255.40  
  Purchase #7 $58.89   11.187%   $65.478   $65.48   $65.50   $65.50  
  7 purchase totals = $770.91       $835.4400   $835.44   $835.40   $835.50