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 $54.30   13.430%   $61.5925   $61.59   $61.60   $61.60  
  Purchase #2 $181.46   12.706%   $204.5163   $204.52   $204.50   $204.50  
  Purchase #3 $249.62   7.587%   $268.5587   $268.56   $268.55   $268.60  
  Purchase #4 $13.93   7.313%   $14.9487   $14.95   $14.95   $14.90  
  Purchase #5 $208.55   8.456%   $226.185   $226.19   $226.20   $226.20  
  Purchase #6 $72.87   5.303%   $76.7343   $76.73   $76.75   $76.70  
  Purchase #7 $216.46   5.507%   $228.3805   $228.38   $228.40   $228.40  
  7 purchase totals = $997.19       $1,080.9160   $1,080.92   $1,080.95   $1,080.90