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 $67.48   13.726%   $76.7423   $76.74   $76.75   $76.70  
  Purchase #2 $131.65   7.115%   $141.0169   $141.02   $141.00   $141.00  
  Purchase #3 $180.40   4.419%   $188.3719   $188.37   $188.35   $188.40  
  Purchase #4 $132.67   4.378%   $138.4783   $138.48   $138.50   $138.50  
  Purchase #5 $5.64   10.356%   $6.2241   $6.22   $6.20   $6.20  
  Purchase #6 $141.36   11.709%   $157.9118   $157.91   $157.90   $157.90  
  Purchase #7 $9.98   3.295%   $10.3088   $10.31   $10.30   $10.30  
  7 purchase totals = $669.18       $719.0541   $719.05   $719.00   $719.00