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 $24.47   8.590%   $26.572   $26.57   $26.55   $26.60  
  Purchase #2 $67.51   8.336%   $73.1376   $73.14   $73.15   $73.10  
  Purchase #3 $158.40   10.742%   $175.4153   $175.42   $175.40   $175.40  
  Purchase #4 $203.56   8.386%   $220.6305   $220.63   $220.65   $220.60  
  Purchase #5 $162.87   6.593%   $173.608   $173.61   $173.60   $173.60  
  Purchase #6 $121.40   4.793%   $127.2187   $127.22   $127.20   $127.20  
  Purchase #7 $29.90   5.863%   $31.653   $31.65   $31.65   $31.70  
  7 purchase totals = $768.11       $828.2351   $828.24   $828.20   $828.20