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 $73.33   6.667%   $78.2189   $78.22   $78.20   $78.20  
  Purchase #2 $22.44   6.404%   $23.8771   $23.88   $23.90   $23.90  
  Purchase #3 $68.56   11.567%   $76.4903   $76.49   $76.50   $76.50  
  Purchase #4 $77.48   9.566%   $84.8917   $84.89   $84.90   $84.90  
  Purchase #5 $204.55   6.104%   $217.0357   $217.04   $217.05   $217.00  
  Purchase #6 $234.36   3.137%   $241.7119   $241.71   $241.70   $241.70  
  Purchase #7 $65.32   11.159%   $72.6091   $72.61   $72.60   $72.60  
  7 purchase totals = $746.04       $794.8347   $794.84   $794.85   $794.80