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 $30.41   8.392%   $32.962   $32.96   $32.95   $33.00  
  Purchase #2 $82.54   11.707%   $92.203   $92.20   $92.20   $92.20  
  Purchase #3 $167.63   6.631%   $178.7455   $178.75   $178.75   $178.70  
  Purchase #4 $171.73   7.662%   $184.888   $184.89   $184.90   $184.90  
  Purchase #5 $160.96   13.354%   $182.4546   $182.45   $182.45   $182.50  
  Purchase #6 $16.78   5.313%   $17.6715   $17.67   $17.65   $17.70  
  Purchase #7 $65.59   10.330%   $72.3654   $72.37   $72.35   $72.40  
  7 purchase totals = $695.64       $761.2900   $761.29   $761.25   $761.40