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 $35.69   8.613%   $38.764   $38.76   $38.75   $38.80  
  Purchase #2 $154.27   13.873%   $175.6719   $175.67   $175.65   $175.70  
  Purchase #3 $71.67   9.682%   $78.6091   $78.61   $78.60   $78.60  
  Purchase #4 $190.29   7.577%   $204.7083   $204.71   $204.70   $204.70  
  Purchase #5 $110.55   8.698%   $120.1656   $120.17   $120.15   $120.20  
  Purchase #6 $205.39   5.523%   $216.7337   $216.73   $216.75   $216.70  
  Purchase #7 $99.64   13.828%   $113.4182   $113.42   $113.40   $113.40  
  7 purchase totals = $867.50       $948.0708   $948.07   $948.00   $948.10