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 $46.97   5.767%   $49.6788   $49.68   $49.70   $49.70  
  Purchase #2 $17.53   6.699%   $18.7043   $18.70   $18.70   $18.70  
  Purchase #3 $205.30   10.575%   $227.0105   $227.01   $227.00   $227.00  
  Purchase #4 $162.70   8.804%   $177.0241   $177.02   $177.00   $177.00  
  Purchase #5 $168.30   12.602%   $189.5092   $189.51   $189.50   $189.50  
  Purchase #6 $91.66   6.725%   $97.8241   $97.82   $97.80   $97.80  
  Purchase #7 $175.85   5.217%   $185.0241   $185.02   $185.00   $185.00  
  7 purchase totals = $868.31       $944.7751   $944.76   $944.70   $944.70