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 $62.53   8.130%   $67.6137   $67.61   $67.60   $67.60  
  Purchase #2 $178.66   10.734%   $197.8374   $197.84   $197.85   $197.80  
  Purchase #3 $46.51   11.768%   $51.9833   $51.98   $52.00   $52.00  
  Purchase #4 $98.93   11.332%   $110.1407   $110.14   $110.15   $110.10  
  Purchase #5 $231.71   7.331%   $248.6967   $248.70   $248.70   $248.70  
  Purchase #6 $15.42   4.391%   $16.0971   $16.10   $16.10   $16.10  
  Purchase #7 $144.81   9.728%   $158.8971   $158.90   $158.90   $158.90  
  7 purchase totals = $778.57       $851.2660   $851.27   $851.30   $851.20