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 $62.67   4.657%   $65.5885   $65.59   $65.60   $65.60  
  Purchase #2 $173.93   13.757%   $197.8576   $197.86   $197.85   $197.90  
  Purchase #3 $18.29   7.191%   $19.6052   $19.61   $19.60   $19.60  
  Purchase #4 $19.41   9.544%   $21.2625   $21.26   $21.25   $21.30  
  Purchase #5 $99.95   4.230%   $104.1779   $104.18   $104.20   $104.20  
  Purchase #6 $87.99   8.341%   $95.3292   $95.33   $95.35   $95.30  
  Purchase #7 $206.90   6.240%   $219.8106   $219.81   $219.80   $219.80  
  7 purchase totals = $669.14       $723.6315   $723.64   $723.65   $723.70