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 $166.53   10.334%   $183.7392   $183.74   $183.75   $183.70  
  Purchase #2 $210.45   12.733%   $237.2466   $237.25   $237.25   $237.20  
  Purchase #3 $104.69   5.482%   $110.4291   $110.43   $110.45   $110.40  
  Purchase #4 $122.87   11.449%   $136.9374   $136.94   $136.95   $136.90  
  Purchase #5 $179.33   13.286%   $203.1558   $203.16   $203.15   $203.20  
  Purchase #6 $57.72   12.596%   $64.9904   $64.99   $65.00   $65.00  
  Purchase #7 $25.65   6.612%   $27.346   $27.35   $27.35   $27.30  
  7 purchase totals = $867.24       $963.8445   $963.86   $963.90   $963.70