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 $79.73   11.292%   $88.7331   $88.73   $88.75   $88.70  
  Purchase #2 $198.51   5.471%   $209.3705   $209.37   $209.35   $209.40  
  Purchase #3 $228.33   4.175%   $237.8628   $237.86   $237.85   $237.90  
  Purchase #4 $162.90   8.823%   $177.2727   $177.27   $177.25   $177.30  
  Purchase #5 $68.60   9.733%   $75.2768   $75.28   $75.30   $75.30  
  Purchase #6 $113.97   11.422%   $126.9877   $126.99   $127.00   $127.00  
  Purchase #7 $131.78   6.563%   $140.4287   $140.43   $140.45   $140.40  
  7 purchase totals = $983.82       $1,055.9323   $1,055.93   $1,055.95   $1,056.00