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 $228.78   11.168%   $254.3302   $254.33   $254.35   $254.30  
  Purchase #2 $236.29   8.507%   $256.3912   $256.39   $256.40   $256.40  
  Purchase #3 $73.76   11.818%   $82.477   $82.48   $82.50   $82.50  
  Purchase #4 $106.36   10.197%   $117.2055   $117.21   $117.20   $117.20  
  Purchase #5 $233.96   7.680%   $251.9281   $251.93   $251.95   $251.90  
  Purchase #6 $67.51   7.598%   $72.6394   $72.64   $72.65   $72.60  
  Purchase #7 $195.96   5.216%   $206.1813   $206.18   $206.20   $206.20  
  7 purchase totals = $1,142.62       $1,241.1527   $1,241.16   $1,241.25   $1,241.10