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 $171.93   6.750%   $183.5353   $183.54   $183.55   $183.50  
  Purchase #2 $232.26   13.111%   $262.7116   $262.71   $262.70   $262.70  
  Purchase #3 $137.56   12.296%   $154.4744   $154.47   $154.45   $154.50  
  Purchase #4 $191.45   13.528%   $217.3494   $217.35   $217.35   $217.30  
  Purchase #5 $55.41   11.420%   $61.7378   $61.74   $61.75   $61.70  
  Purchase #6 $178.91   13.333%   $202.7641   $202.76   $202.75   $202.80  
  Purchase #7 $100.81   12.298%   $113.2076   $113.21   $113.20   $113.20  
  7 purchase totals = $1,068.33       $1,195.7802   $1,195.78   $1,195.75   $1,195.70