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 $183.64   8.203%   $198.704   $198.70   $198.70   $198.70  
  Purchase #2 $113.84   11.187%   $126.5753   $126.58   $126.60   $126.60  
  Purchase #3 $194.89   3.866%   $202.4244   $202.42   $202.40   $202.40  
  Purchase #4 $159.75   8.127%   $172.7329   $172.73   $172.75   $172.70  
  Purchase #5 $142.33   6.760%   $151.9515   $151.95   $151.95   $152.00  
  Purchase #6 $34.45   5.427%   $36.3196   $36.32   $36.30   $36.30  
  Purchase #7 $71.26   4.593%   $74.533   $74.53   $74.55   $74.50  
  7 purchase totals = $900.16       $963.2407   $963.23   $963.25   $963.20