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 $133.63   12.369%   $150.1587   $150.16   $150.15   $150.20  
  Purchase #2 $240.97   5.219%   $253.5462   $253.55   $253.55   $253.50  
  Purchase #3 $161.54   3.538%   $167.2553   $167.26   $167.25   $167.30  
  Purchase #4 $62.44   11.482%   $69.6094   $69.61   $69.60   $69.60  
  Purchase #5 $150.84   4.228%   $157.2175   $157.22   $157.20   $157.20  
  Purchase #6 $218.85   7.243%   $234.7013   $234.70   $234.70   $234.70  
  Purchase #7 $191.30   4.544%   $199.9927   $199.99   $200.00   $200.00  
  7 purchase totals = $1,159.57       $1,232.4811   $1,232.49   $1,232.45   $1,232.50