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 $229.89   13.225%   $260.293   $260.29   $260.30   $260.30  
  Purchase #2 $103.62   9.476%   $113.439   $113.44   $113.45   $113.40  
  Purchase #3 $168.59   8.520%   $182.9539   $182.95   $182.95   $183.00  
  Purchase #4 $166.97   6.381%   $177.6244   $177.62   $177.60   $177.60  
  Purchase #5 $60.33   3.226%   $62.2762   $62.28   $62.30   $62.30  
  Purchase #6 $47.52   5.222%   $50.0015   $50.00   $50.00   $50.00  
  Purchase #7 $89.72   13.713%   $102.0233   $102.02   $102.00   $102.00  
  7 purchase totals = $866.64       $948.6113   $948.60   $948.60   $948.60