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 $61.72   4.873%   $64.7276   $64.73   $64.75   $64.70  
  Purchase #2 $184.43   12.580%   $207.6313   $207.63   $207.65   $207.60  
  Purchase #3 $242.61   5.266%   $255.3858   $255.39   $255.40   $255.40  
  Purchase #4 $238.85   6.431%   $254.2104   $254.21   $254.20   $254.20  
  Purchase #5 $59.26   6.540%   $63.1356   $63.14   $63.15   $63.10  
  Purchase #6 $5.47   12.309%   $6.1433   $6.14   $6.15   $6.10  
  Purchase #7 $92.26   6.860%   $98.589   $98.59   $98.60   $98.60  
  7 purchase totals = $884.60       $949.8230   $949.83   $949.90   $949.70