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 $181.87   13.318%   $206.0914   $206.09   $206.10   $206.10  
  Purchase #2 $76.43   10.217%   $84.2389   $84.24   $84.25   $84.20  
  Purchase #3 $179.68   11.333%   $200.0431   $200.04   $200.05   $200.00  
  Purchase #4 $70.29   8.523%   $76.2808   $76.28   $76.30   $76.30  
  Purchase #5 $217.51   4.698%   $227.7286   $227.73   $227.75   $227.70  
  Purchase #6 $210.90   12.519%   $237.3026   $237.30   $237.30   $237.30  
  Purchase #7 $27.39   10.167%   $30.1747   $30.17   $30.15   $30.20  
  7 purchase totals = $964.07       $1,061.8601   $1,061.85   $1,061.90   $1,061.80