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 $66.63   11.792%   $74.487   $74.49   $74.50   $74.50  
  Purchase #2 $167.75   8.656%   $182.2704   $182.27   $182.25   $182.30  
  Purchase #3 $246.58   9.391%   $269.7363   $269.74   $269.75   $269.70  
  Purchase #4 $108.67   13.287%   $123.109   $123.11   $123.10   $123.10  
  Purchase #5 $163.75   5.118%   $172.1307   $172.13   $172.15   $172.10  
  Purchase #6 $60.94   5.272%   $64.1528   $64.15   $64.15   $64.20  
  Purchase #7 $68.69   12.232%   $77.0922   $77.09   $77.10   $77.10  
  7 purchase totals = $883.01       $962.9784   $962.98   $963.00   $963.00