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 $59.83   8.468%   $64.8964   $64.90   $64.90   $64.90  
  Purchase #2 $94.87   9.501%   $103.8836   $103.88   $103.90   $103.90  
  Purchase #3 $115.62   3.419%   $119.573   $119.57   $119.55   $119.60  
  Purchase #4 $36.34   11.311%   $40.4504   $40.45   $40.45   $40.50  
  Purchase #5 $26.59   8.397%   $28.8228   $28.82   $28.80   $28.80  
  Purchase #6 $103.54   3.830%   $107.5056   $107.51   $107.50   $107.50  
  Purchase #7 $27.45   5.549%   $28.9732   $28.97   $28.95   $29.00  
  7 purchase totals = $464.24       $494.1050   $494.10   $494.05   $494.20