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 $22.63   8.819%   $24.6257   $24.63   $24.65   $24.60  
  Purchase #2 $241.86   5.170%   $254.3642   $254.36   $254.35   $254.40  
  Purchase #3 $151.80   4.718%   $158.9619   $158.96   $158.95   $159.00  
  Purchase #4 $99.39   8.272%   $107.6115   $107.61   $107.60   $107.60  
  Purchase #5 $153.33   5.765%   $162.1695   $162.17   $162.15   $162.20  
  Purchase #6 $29.32   12.506%   $32.9868   $32.99   $33.00   $33.00  
  Purchase #7 $28.56   7.291%   $30.6423   $30.64   $30.65   $30.60  
  7 purchase totals = $726.89       $771.3619   $771.36   $771.35   $771.40