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 $56.94   4.584%   $59.5501   $59.55   $59.55   $59.60  
  Purchase #2 $6.69   6.245%   $7.1078   $7.11   $7.10   $7.10  
  Purchase #3 $198.71   8.831%   $216.2581   $216.26   $216.25   $216.30  
  Purchase #4 $224.50   3.576%   $232.5281   $232.53   $232.55   $232.50  
  Purchase #5 $97.61   4.139%   $101.6501   $101.65   $101.65   $101.70  
  Purchase #6 $49.41   4.639%   $51.7021   $51.70   $51.70   $51.70  
  Purchase #7 $119.81   7.646%   $128.9707   $128.97   $128.95   $129.00  
  7 purchase totals = $753.67       $797.7670   $797.77   $797.75   $797.90