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 $24.48   3.462%   $25.3275   $25.33   $25.35   $25.30  
  Purchase #2 $217.86   11.417%   $242.7331   $242.73   $242.75   $242.70  
  Purchase #3 $190.85   10.677%   $211.2271   $211.23   $211.25   $211.20  
  Purchase #4 $127.92   4.796%   $134.055   $134.06   $134.05   $134.10  
  Purchase #5 $12.49   10.833%   $13.843   $13.84   $13.85   $13.80  
  Purchase #6 $178.88   8.518%   $194.117   $194.12   $194.10   $194.10  
  Purchase #7 $12.69   7.182%   $13.6014   $13.60   $13.60   $13.60  
  7 purchase totals = $765.17       $834.9041   $834.91   $834.95   $834.80