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 $235.68   11.178%   $262.0243   $262.02   $262.00   $262.00  
  Purchase #2 $106.73   10.662%   $118.1096   $118.11   $118.10   $118.10  
  Purchase #3 $129.29   8.302%   $140.0237   $140.02   $140.00   $140.00  
  Purchase #4 $212.86   11.787%   $237.9498   $237.95   $237.95   $237.90  
  Purchase #5 $158.85   4.394%   $165.8299   $165.83   $165.85   $165.80  
  Purchase #6 $199.99   6.185%   $212.3594   $212.36   $212.35   $212.40  
  Purchase #7 $186.91   11.766%   $208.9018   $208.90   $208.90   $208.90  
  7 purchase totals = $1,230.31       $1,345.1985   $1,345.19   $1,345.15   $1,345.10