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 $69.53   8.559%   $75.4811   $75.48   $75.50   $75.50  
  Purchase #2 $61.63   6.467%   $65.6156   $65.62   $65.60   $65.60  
  Purchase #3 $52.95   3.431%   $54.7667   $54.77   $54.75   $54.80  
  Purchase #4 $215.55   9.414%   $235.8419   $235.84   $235.85   $235.80  
  Purchase #5 $216.87   5.686%   $229.2012   $229.20   $229.20   $229.20  
  Purchase #6 $163.53   11.363%   $182.1119   $182.11   $182.10   $182.10  
  Purchase #7 $12.70   8.752%   $13.8115   $13.81   $13.80   $13.80  
  7 purchase totals = $792.76       $856.8299   $856.83   $856.80   $856.80