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 $244.35   7.219%   $261.9896   $261.99   $262.00   $262.00  
  Purchase #2 $120.43   11.126%   $133.829   $133.83   $133.85   $133.80  
  Purchase #3 $158.26   8.107%   $171.0901   $171.09   $171.10   $171.10  
  Purchase #4 $149.75   10.496%   $165.4678   $165.47   $165.45   $165.50  
  Purchase #5 $74.89   11.847%   $83.7622   $83.76   $83.75   $83.80  
  Purchase #6 $158.84   11.396%   $176.9414   $176.94   $176.95   $176.90  
  Purchase #7 $44.33   4.679%   $46.4042   $46.40   $46.40   $46.40  
  7 purchase totals = $950.85       $1,039.4843   $1,039.48   $1,039.50   $1,039.50