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 $57.94   11.604%   $64.6634   $64.66   $64.65   $64.70  
  Purchase #2 $24.41   3.347%   $25.227   $25.23   $25.25   $25.20  
  Purchase #3 $189.67   12.797%   $213.9421   $213.94   $213.95   $213.90  
  Purchase #4 $190.30   13.536%   $216.059   $216.06   $216.05   $216.10  
  Purchase #5 $13.26   8.850%   $14.4335   $14.43   $14.45   $14.40  
  Purchase #6 $242.89   13.612%   $275.9522   $275.95   $275.95   $276.00  
  Purchase #7 $64.76   6.511%   $68.9765   $68.98   $69.00   $69.00  
  7 purchase totals = $783.23       $879.2537   $879.25   $879.30   $879.30