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 $57.50   8.846%   $62.5865   $62.59   $62.60   $62.60  
  Purchase #2 $96.48   8.562%   $104.7406   $104.74   $104.75   $104.70  
  Purchase #3 $249.66   11.385%   $278.0838   $278.08   $278.10   $278.10  
  Purchase #4 $21.32   13.791%   $24.2602   $24.26   $24.25   $24.30  
  Purchase #5 $36.74   10.606%   $40.6366   $40.64   $40.65   $40.60  
  Purchase #6 $101.69   8.313%   $110.1435   $110.14   $110.15   $110.10  
  Purchase #7 $29.92   7.609%   $32.1966   $32.20   $32.20   $32.20  
  7 purchase totals = $593.31       $652.6478   $652.65   $652.70   $652.60