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 $119.69   10.738%   $132.5423   $132.54   $132.55   $132.50  
  Purchase #2 $17.27   8.823%   $18.7937   $18.79   $18.80   $18.80  
  Purchase #3 $173.55   7.117%   $185.9016   $185.90   $185.90   $185.90  
  Purchase #4 $94.28   13.226%   $106.7495   $106.75   $106.75   $106.70  
  Purchase #5 $99.47   13.406%   $112.8049   $112.80   $112.80   $112.80  
  Purchase #6 $237.50   9.740%   $260.6325   $260.63   $260.65   $260.60  
  Purchase #7 $219.34   9.370%   $239.8922   $239.89   $239.90   $239.90  
  7 purchase totals = $961.10       $1,057.3167   $1,057.30   $1,057.35   $1,057.20