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 $76.36   9.355%   $83.5035   $83.50   $83.50   $83.50  
  Purchase #2 $14.36   11.541%   $16.0173   $16.02   $16.00   $16.00  
  Purchase #3 $193.76   3.720%   $200.9679   $200.97   $200.95   $201.00  
  Purchase #4 $98.32   3.459%   $101.7209   $101.72   $101.70   $101.70  
  Purchase #5 $226.74   7.844%   $244.5255   $244.53   $244.55   $244.50  
  Purchase #6 $60.87   9.219%   $66.4816   $66.48   $66.50   $66.50  
  Purchase #7 $44.78   8.517%   $48.5939   $48.59   $48.60   $48.60  
  7 purchase totals = $715.19       $761.8106   $761.81   $761.80   $761.80