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 $29.38   11.472%   $32.7505   $32.75   $32.75   $32.80  
  Purchase #2 $51.88   13.647%   $58.9601   $58.96   $58.95   $59.00  
  Purchase #3 $24.36   6.655%   $25.9812   $25.98   $26.00   $26.00  
  Purchase #4 $50.44   12.258%   $56.6229   $56.62   $56.60   $56.60  
  Purchase #5 $141.55   5.838%   $149.8137   $149.81   $149.80   $149.80  
  Purchase #6 $115.49   9.381%   $126.3241   $126.32   $126.30   $126.30  
  Purchase #7 $56.91   7.234%   $61.0269   $61.03   $61.05   $61.00  
  7 purchase totals = $470.01       $511.4794   $511.47   $511.45   $511.50