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 $48.65   12.151%   $54.5615   $54.56   $54.55   $54.60  
  Purchase #2 $180.71   4.543%   $188.9197   $188.92   $188.90   $188.90  
  Purchase #3 $57.36   7.319%   $61.5582   $61.56   $61.55   $61.60  
  Purchase #4 $204.25   11.326%   $227.3834   $227.38   $227.40   $227.40  
  Purchase #5 $119.53   5.541%   $126.1532   $126.15   $126.15   $126.20  
  Purchase #6 $117.57   10.573%   $130.0007   $130.00   $130.00   $130.00  
  Purchase #7 $121.78   5.525%   $128.5083   $128.51   $128.50   $128.50  
  7 purchase totals = $849.85       $917.0850   $917.08   $917.05   $917.20