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 $180.93   7.771%   $194.9901   $194.99   $195.00   $195.00  
  Purchase #2 $215.74   12.170%   $241.9956   $242.00   $242.00   $242.00  
  Purchase #3 $210.73   8.190%   $227.9888   $227.99   $228.00   $228.00  
  Purchase #4 $222.63   7.169%   $238.5903   $238.59   $238.60   $238.60  
  Purchase #5 $34.97   3.494%   $36.1919   $36.19   $36.20   $36.20  
  Purchase #6 $10.25   9.727%   $11.247   $11.25   $11.25   $11.20  
  Purchase #7 $15.31   5.410%   $16.1383   $16.14   $16.15   $16.10  
  7 purchase totals = $890.56       $967.1420   $967.15   $967.20   $967.10