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 $18.28   10.766%   $20.248   $20.25   $20.25   $20.20  
  Purchase #2 $240.79   10.105%   $265.1218   $265.12   $265.10   $265.10  
  Purchase #3 $7.56   10.216%   $8.3323   $8.33   $8.35   $8.30  
  Purchase #4 $243.79   4.794%   $255.4773   $255.48   $255.50   $255.50  
  Purchase #5 $15.74   10.567%   $17.4032   $17.40   $17.40   $17.40  
  Purchase #6 $190.27   7.383%   $204.3176   $204.32   $204.30   $204.30  
  Purchase #7 $121.98   12.460%   $137.1787   $137.18   $137.20   $137.20  
  7 purchase totals = $838.41       $908.0789   $908.08   $908.10   $908.00