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 $74.30   3.504%   $76.9035   $76.90   $76.90   $76.90  
  Purchase #2 $132.99   6.545%   $141.6942   $141.69   $141.70   $141.70  
  Purchase #3 $91.74   3.507%   $94.9573   $94.96   $94.95   $95.00  
  Purchase #4 $77.37   8.195%   $83.7105   $83.71   $83.70   $83.70  
  Purchase #5 $43.82   6.248%   $46.5579   $46.56   $46.55   $46.60  
  Purchase #6 $239.53   8.709%   $260.3907   $260.39   $260.40   $260.40  
  Purchase #7 $88.35   3.191%   $91.1692   $91.17   $91.15   $91.20  
  7 purchase totals = $748.10       $795.3833   $795.38   $795.35   $795.50