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 $111.75   6.484%   $118.9959   $119.00   $119.00   $119.00  
  Purchase #2 $93.97   4.286%   $97.9976   $98.00   $98.00   $98.00  
  Purchase #3 $188.53   6.756%   $201.2671   $201.27   $201.25   $201.30  
  Purchase #4 $127.43   9.298%   $139.2784   $139.28   $139.30   $139.30  
  Purchase #5 $43.48   5.259%   $45.7666   $45.77   $45.75   $45.80  
  Purchase #6 $144.80   12.381%   $162.7277   $162.73   $162.75   $162.70  
  Purchase #7 $204.59   6.353%   $217.5876   $217.59   $217.60   $217.60  
  7 purchase totals = $914.55       $983.6209   $983.64   $983.65   $983.70