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 $182.43   7.391%   $195.9134   $195.91   $195.90   $195.90  
  Purchase #2 $229.77   13.186%   $260.0675   $260.07   $260.05   $260.10  
  Purchase #3 $143.47   3.379%   $148.3179   $148.32   $148.30   $148.30  
  Purchase #4 $136.87   12.178%   $153.538   $153.54   $153.55   $153.50  
  Purchase #5 $211.50   10.282%   $233.2464   $233.25   $233.25   $233.20  
  Purchase #6 $41.54   7.204%   $44.5325   $44.53   $44.55   $44.50  
  Purchase #7 $40.44   10.795%   $44.8055   $44.81   $44.80   $44.80  
  7 purchase totals = $986.02       $1,080.4212   $1,080.43   $1,080.40   $1,080.30