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 $188.97   7.157%   $202.4946   $202.49   $202.50   $202.50  
  Purchase #2 $172.98   3.266%   $178.6295   $178.63   $178.65   $178.60  
  Purchase #3 $126.32   6.733%   $134.8251   $134.83   $134.85   $134.80  
  Purchase #4 $230.84   6.329%   $245.4499   $245.45   $245.45   $245.40  
  Purchase #5 $205.47   6.398%   $218.616   $218.62   $218.60   $218.60  
  Purchase #6 $206.99   3.618%   $214.4789   $214.48   $214.50   $214.50  
  Purchase #7 $53.57   10.751%   $59.3293   $59.33   $59.35   $59.30  
  7 purchase totals = $1,185.14       $1,253.8233   $1,253.83   $1,253.90   $1,253.70