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 $149.73   11.662%   $167.1915   $167.19   $167.20   $167.20  
  Purchase #2 $87.36   8.484%   $94.7716   $94.77   $94.75   $94.80  
  Purchase #3 $50.43   13.312%   $57.1432   $57.14   $57.15   $57.10  
  Purchase #4 $75.89   12.392%   $85.2943   $85.29   $85.30   $85.30  
  Purchase #5 $13.82   10.313%   $15.2453   $15.25   $15.25   $15.20  
  Purchase #6 $115.87   12.795%   $130.6956   $130.70   $130.70   $130.70  
  Purchase #7 $208.65   6.344%   $221.8868   $221.89   $221.90   $221.90  
  7 purchase totals = $701.75       $772.2283   $772.23   $772.25   $772.20