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 $69.55   6.363%   $73.9755   $73.98   $74.00   $74.00  
  Purchase #2 $151.38   6.149%   $160.6884   $160.69   $160.70   $160.70  
  Purchase #3 $90.75   13.413%   $102.9223   $102.92   $102.90   $102.90  
  Purchase #4 $238.92   9.582%   $261.8133   $261.81   $261.80   $261.80  
  Purchase #5 $123.37   10.644%   $136.5015   $136.50   $136.50   $136.50  
  Purchase #6 $36.82   13.193%   $41.6777   $41.68   $41.70   $41.70  
  Purchase #7 $134.79   8.141%   $145.7633   $145.76   $145.75   $145.80  
  7 purchase totals = $845.58       $923.3420   $923.34   $923.35   $923.40