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 $60.63   12.729%   $68.3476   $68.35   $68.35   $68.30  
  Purchase #2 $39.58   13.860%   $45.0658   $45.07   $45.05   $45.10  
  Purchase #3 $179.79   4.735%   $188.3031   $188.30   $188.30   $188.30  
  Purchase #4 $32.76   8.108%   $35.4162   $35.42   $35.40   $35.40  
  Purchase #5 $230.90   13.829%   $262.8312   $262.83   $262.85   $262.80  
  Purchase #6 $216.62   12.747%   $244.2326   $244.23   $244.25   $244.20  
  Purchase #7 $90.90   10.788%   $100.7063   $100.71   $100.70   $100.70  
  7 purchase totals = $851.18       $944.9028   $944.91   $944.90   $944.80