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 $87.75   10.793%   $97.2209   $97.22   $97.20   $97.20  
  Purchase #2 $94.38   13.809%   $107.4129   $107.41   $107.40   $107.40  
  Purchase #3 $31.40   13.800%   $35.7332   $35.73   $35.75   $35.70  
  Purchase #4 $229.81   10.249%   $253.3632   $253.36   $253.35   $253.40  
  Purchase #5 $239.44   12.319%   $268.9366   $268.94   $268.95   $268.90  
  Purchase #6 $148.84   3.176%   $153.5672   $153.57   $153.55   $153.60  
  Purchase #7 $158.42   13.343%   $179.558   $179.56   $179.55   $179.60  
  7 purchase totals = $990.04       $1,095.7920   $1,095.79   $1,095.75   $1,095.80