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 $121.61   4.687%   $127.3099   $127.31   $127.30   $127.30  
  Purchase #2 $241.41   4.327%   $251.8558   $251.86   $251.85   $251.90  
  Purchase #3 $185.78   4.575%   $194.2794   $194.28   $194.30   $194.30  
  Purchase #4 $236.95   5.151%   $249.1553   $249.16   $249.15   $249.20  
  Purchase #5 $129.49   4.242%   $134.983   $134.98   $135.00   $135.00  
  Purchase #6 $220.94   9.249%   $241.3747   $241.37   $241.35   $241.40  
  Purchase #7 $224.35   10.428%   $247.7452   $247.75   $247.75   $247.70  
  7 purchase totals = $1,360.53       $1,446.7033   $1,446.71   $1,446.70   $1,446.80