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 $131.66   11.619%   $146.9576   $146.96   $146.95   $147.00  
  Purchase #2 $221.39   5.145%   $232.7805   $232.78   $232.80   $232.80  
  Purchase #3 $86.77   3.507%   $89.813   $89.81   $89.80   $89.80  
  Purchase #4 $84.80   10.613%   $93.7998   $93.80   $93.80   $93.80  
  Purchase #5 $175.52   11.417%   $195.5591   $195.56   $195.55   $195.60  
  Purchase #6 $107.42   8.871%   $116.9492   $116.95   $116.95   $116.90  
  Purchase #7 $94.48   8.818%   $102.8112   $102.81   $102.80   $102.80  
  7 purchase totals = $902.04       $978.6704   $978.67   $978.65   $978.70