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 $68.80   8.551%   $74.6831   $74.68   $74.70   $74.70  
  Purchase #2 $233.98   8.230%   $253.2366   $253.24   $253.25   $253.20  
  Purchase #3 $24.94   11.117%   $27.7126   $27.71   $27.70   $27.70  
  Purchase #4 $229.95   8.496%   $249.4866   $249.49   $249.50   $249.50  
  Purchase #5 $159.98   4.844%   $167.7294   $167.73   $167.75   $167.70  
  Purchase #6 $47.66   9.473%   $52.1748   $52.17   $52.15   $52.20  
  Purchase #7 $229.45   13.185%   $259.703   $259.70   $259.70   $259.70  
  7 purchase totals = $994.76       $1,084.7261   $1,084.72   $1,084.75   $1,084.70