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 $107.54   10.661%   $119.0048   $119.00   $119.00   $119.00  
  Purchase #2 $55.87   3.761%   $57.9713   $57.97   $57.95   $58.00  
  Purchase #3 $152.70   12.502%   $171.7906   $171.79   $171.80   $171.80  
  Purchase #4 $67.85   11.292%   $75.5116   $75.51   $75.50   $75.50  
  Purchase #5 $52.61   7.255%   $56.4269   $56.43   $56.45   $56.40  
  Purchase #6 $146.32   8.501%   $158.7587   $158.76   $158.75   $158.80  
  Purchase #7 $244.98   5.267%   $257.8831   $257.88   $257.90   $257.90  
  7 purchase totals = $827.87       $897.3470   $897.34   $897.35   $897.40