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 $61.81   5.123%   $64.9765   $64.98   $65.00   $65.00  
  Purchase #2 $215.85   4.866%   $226.3533   $226.35   $226.35   $226.40  
  Purchase #3 $55.34   4.462%   $57.8093   $57.81   $57.80   $57.80  
  Purchase #4 $190.54   12.244%   $213.8697   $213.87   $213.85   $213.90  
  Purchase #5 $25.73   11.871%   $28.7844   $28.78   $28.80   $28.80  
  Purchase #6 $47.45   8.235%   $51.3575   $51.36   $51.35   $51.40  
  Purchase #7 $63.58   10.408%   $70.1974   $70.20   $70.20   $70.20  
  7 purchase totals = $660.30       $713.3481   $713.35   $713.35   $713.50