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 $169.94   8.645%   $184.6313   $184.63   $184.65   $184.60  
  Purchase #2 $214.67   12.569%   $241.6519   $241.65   $241.65   $241.70  
  Purchase #3 $200.93   10.429%   $221.885   $221.89   $221.90   $221.90  
  Purchase #4 $220.62   4.217%   $229.9235   $229.92   $229.90   $229.90  
  Purchase #5 $101.61   7.106%   $108.8304   $108.83   $108.85   $108.80  
  Purchase #6 $81.78   3.396%   $84.5572   $84.56   $84.55   $84.60  
  Purchase #7 $119.63   12.650%   $134.7632   $134.76   $134.75   $134.80  
  7 purchase totals = $1,109.18       $1,206.2425   $1,206.24   $1,206.25   $1,206.30