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 $22.56   9.529%   $24.7097   $24.71   $24.70   $24.70  
  Purchase #2 $191.53   5.132%   $201.3593   $201.36   $201.35   $201.40  
  Purchase #3 $39.99   6.355%   $42.5314   $42.53   $42.55   $42.50  
  Purchase #4 $118.56   4.596%   $124.009   $124.01   $124.00   $124.00  
  Purchase #5 $234.80   11.776%   $262.45   $262.45   $262.45   $262.50  
  Purchase #6 $39.79   11.583%   $44.3989   $44.40   $44.40   $44.40  
  Purchase #7 $68.51   4.289%   $71.4484   $71.45   $71.45   $71.40  
  7 purchase totals = $715.74       $770.9067   $770.91   $770.90   $770.90