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 $229.71   3.821%   $238.4872   $238.49   $238.50   $238.50  
  Purchase #2 $63.99   4.667%   $66.9764   $66.98   $67.00   $67.00  
  Purchase #3 $247.64   11.758%   $276.7575   $276.76   $276.75   $276.80  
  Purchase #4 $154.82   7.396%   $166.2705   $166.27   $166.25   $166.30  
  Purchase #5 $37.26   5.316%   $39.2407   $39.24   $39.25   $39.20  
  Purchase #6 $221.25   11.108%   $245.8265   $245.83   $245.85   $245.80  
  Purchase #7 $154.97   5.735%   $163.8575   $163.86   $163.85   $163.90  
  7 purchase totals = $1,109.64       $1,197.4163   $1,197.43   $1,197.45   $1,197.50