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 $249.58   5.709%   $263.8285   $263.83   $263.85   $263.80  
  Purchase #2 $153.36   11.792%   $171.4442   $171.44   $171.45   $171.40  
  Purchase #3 $191.95   13.192%   $217.272   $217.27   $217.25   $217.30  
  Purchase #4 $161.91   11.436%   $180.426   $180.43   $180.45   $180.40  
  Purchase #5 $161.95   13.674%   $184.095   $184.10   $184.10   $184.10  
  Purchase #6 $194.49   6.600%   $207.3263   $207.33   $207.35   $207.30  
  Purchase #7 $53.89   8.338%   $58.3833   $58.38   $58.40   $58.40  
  7 purchase totals = $1,167.13       $1,282.7753   $1,282.78   $1,282.85   $1,282.70