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 $61.43   6.413%   $65.3695   $65.37   $65.35   $65.40  
  Purchase #2 $65.87   12.439%   $74.0636   $74.06   $74.05   $74.10  
  Purchase #3 $23.32   10.650%   $25.8036   $25.80   $25.80   $25.80  
  Purchase #4 $195.46   10.484%   $215.952   $215.95   $215.95   $216.00  
  Purchase #5 $177.30   9.220%   $193.6471   $193.65   $193.65   $193.60  
  Purchase #6 $146.89   5.272%   $154.634   $154.63   $154.65   $154.60  
  Purchase #7 $145.38   4.777%   $152.3248   $152.32   $152.30   $152.30  
  7 purchase totals = $815.65       $881.7946   $881.78   $881.75   $881.80