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 $104.99   7.872%   $113.2548   $113.25   $113.25   $113.30  
  Purchase #2 $172.76   5.485%   $182.2359   $182.24   $182.25   $182.20  
  Purchase #3 $63.92   10.336%   $70.5268   $70.53   $70.55   $70.50  
  Purchase #4 $106.39   12.742%   $119.9462   $119.95   $119.95   $119.90  
  Purchase #5 $129.90   3.843%   $134.8921   $134.89   $134.90   $134.90  
  Purchase #6 $211.70   6.224%   $224.8762   $224.88   $224.90   $224.90  
  Purchase #7 $139.73   6.839%   $149.2861   $149.29   $149.30   $149.30  
  7 purchase totals = $929.39       $995.0181   $995.03   $995.10   $995.00