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 $56.76   9.159%   $61.9586   $61.96   $61.95   $62.00  
  Purchase #2 $78.82   7.593%   $84.8048   $84.80   $84.80   $84.80  
  Purchase #3 $6.35   9.718%   $6.9671   $6.97   $6.95   $7.00  
  Purchase #4 $68.73   13.138%   $77.7597   $77.76   $77.75   $77.80  
  Purchase #5 $61.67   10.551%   $68.1768   $68.18   $68.20   $68.20  
  Purchase #6 $73.70   13.180%   $83.4137   $83.41   $83.40   $83.40  
  Purchase #7 $82.62   4.851%   $86.6279   $86.63   $86.65   $86.60  
  7 purchase totals = $428.65       $469.7086   $469.71   $469.70   $469.80