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 $24.63   4.585%   $25.7593   $25.76   $25.75   $25.80  
  Purchase #2 $164.82   11.292%   $183.4315   $183.43   $183.45   $183.40  
  Purchase #3 $228.98   5.732%   $242.1051   $242.11   $242.10   $242.10  
  Purchase #4 $244.79   10.366%   $270.1649   $270.16   $270.15   $270.20  
  Purchase #5 $103.64   9.615%   $113.605   $113.61   $113.60   $113.60  
  Purchase #6 $99.25   3.630%   $102.8528   $102.85   $102.85   $102.90  
  Purchase #7 $22.43   8.561%   $24.3502   $24.35   $24.35   $24.40  
  7 purchase totals = $888.54       $962.2688   $962.27   $962.25   $962.40