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 $66.69   5.680%   $70.478   $70.48   $70.50   $70.50  
  Purchase #2 $120.93   3.323%   $124.9485   $124.95   $124.95   $124.90  
  Purchase #3 $82.92   12.356%   $93.1656   $93.17   $93.15   $93.20  
  Purchase #4 $240.90   4.559%   $251.8826   $251.88   $251.90   $251.90  
  Purchase #5 $98.43   3.407%   $101.7835   $101.78   $101.80   $101.80  
  Purchase #6 $246.26   10.543%   $272.2232   $272.22   $272.20   $272.20  
  Purchase #7 $103.85   8.549%   $112.7281   $112.73   $112.75   $112.70  
  7 purchase totals = $959.98       $1,027.2095   $1,027.21   $1,027.25   $1,027.20