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 $22.44   10.237%   $24.7372   $24.74   $24.75   $24.70  
  Purchase #2 $127.57   10.666%   $141.1766   $141.18   $141.20   $141.20  
  Purchase #3 $34.35   3.502%   $35.5529   $35.55   $35.55   $35.60  
  Purchase #4 $206.86   12.384%   $232.4775   $232.48   $232.50   $232.50  
  Purchase #5 $109.53   6.104%   $116.2157   $116.22   $116.20   $116.20  
  Purchase #6 $158.55   11.253%   $176.3916   $176.39   $176.40   $176.40  
  Purchase #7 $200.94   8.167%   $217.3508   $217.35   $217.35   $217.40  
  7 purchase totals = $860.24       $943.9023   $943.91   $943.95   $944.00