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 $67.86   8.790%   $73.8249   $73.82   $73.80   $73.80  
  Purchase #2 $167.91   10.762%   $185.9805   $185.98   $186.00   $186.00  
  Purchase #3 $71.94   5.545%   $75.9291   $75.93   $75.95   $75.90  
  Purchase #4 $97.63   4.344%   $101.871   $101.87   $101.85   $101.90  
  Purchase #5 $216.63   13.221%   $245.2707   $245.27   $245.25   $245.30  
  Purchase #6 $124.27   5.373%   $130.947   $130.95   $130.95   $130.90  
  Purchase #7 $29.40   11.835%   $32.8795   $32.88   $32.90   $32.90  
  7 purchase totals = $775.64       $846.7027   $846.70   $846.70   $846.70