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 $217.84   12.595%   $245.2769   $245.28   $245.30   $245.30  
  Purchase #2 $205.52   12.265%   $230.727   $230.73   $230.75   $230.70  
  Purchase #3 $54.33   12.213%   $60.9653   $60.97   $60.95   $61.00  
  Purchase #4 $98.92   10.716%   $109.5203   $109.52   $109.50   $109.50  
  Purchase #5 $12.47   3.492%   $12.9055   $12.91   $12.90   $12.90  
  Purchase #6 $52.25   3.313%   $53.981   $53.98   $54.00   $54.00  
  Purchase #7 $225.39   5.536%   $237.8676   $237.87   $237.85   $237.90  
  7 purchase totals = $866.72       $951.2436   $951.26   $951.25   $951.30