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 $84.71   8.789%   $92.1552   $92.16   $92.15   $92.20  
  Purchase #2 $113.42   5.492%   $119.649   $119.65   $119.65   $119.60  
  Purchase #3 $17.72   3.847%   $18.4017   $18.40   $18.40   $18.40  
  Purchase #4 $56.43   10.473%   $62.3399   $62.34   $62.35   $62.30  
  Purchase #5 $103.37   3.389%   $106.8732   $106.87   $106.85   $106.90  
  Purchase #6 $49.78   8.458%   $53.9904   $53.99   $54.00   $54.00  
  Purchase #7 $183.70   8.496%   $199.3072   $199.31   $199.30   $199.30  
  7 purchase totals = $609.13       $652.7166   $652.72   $652.70   $652.70