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 $114.91   9.291%   $125.5863   $125.59   $125.60   $125.60  
  Purchase #2 $202.25   8.738%   $219.9226   $219.92   $219.90   $219.90  
  Purchase #3 $195.93   3.203%   $202.2056   $202.21   $202.20   $202.20  
  Purchase #4 $142.47   10.449%   $157.3567   $157.36   $157.35   $157.40  
  Purchase #5 $225.80   5.237%   $237.6251   $237.63   $237.65   $237.60  
  Purchase #6 $44.83   13.414%   $50.8435   $50.84   $50.85   $50.80  
  Purchase #7 $28.49   9.863%   $31.3   $31.30   $31.30   $31.30  
  7 purchase totals = $954.68       $1,024.8398   $1,024.85   $1,024.85   $1,024.80