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 $41.61   9.255%   $45.461   $45.46   $45.45   $45.50  
  Purchase #2 $105.80   10.354%   $116.7545   $116.75   $116.75   $116.80  
  Purchase #3 $127.49   4.571%   $133.3176   $133.32   $133.30   $133.30  
  Purchase #4 $205.77   5.761%   $217.6244   $217.62   $217.60   $217.60  
  Purchase #5 $247.65   13.516%   $281.1224   $281.12   $281.10   $281.10  
  Purchase #6 $125.25   11.773%   $139.9957   $140.00   $140.00   $140.00  
  Purchase #7 $5.95   12.855%   $6.7149   $6.71   $6.70   $6.70  
  7 purchase totals = $859.52       $940.9905   $940.98   $940.90   $941.00