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 $181.93   10.770%   $201.5239   $201.52   $201.50   $201.50  
  Purchase #2 $50.83   12.249%   $57.0562   $57.06   $57.05   $57.10  
  Purchase #3 $110.45   4.703%   $115.6445   $115.64   $115.65   $115.60  
  Purchase #4 $66.84   5.852%   $70.7515   $70.75   $70.75   $70.80  
  Purchase #5 $110.70   8.680%   $120.3088   $120.31   $120.30   $120.30  
  Purchase #6 $188.72   3.141%   $194.6477   $194.65   $194.65   $194.60  
  Purchase #7 $68.88   10.300%   $75.9746   $75.97   $75.95   $76.00  
  7 purchase totals = $778.35       $835.9072   $835.90   $835.85   $835.90