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 $172.38   13.278%   $195.2686   $195.27   $195.25   $195.30  
  Purchase #2 $229.29   4.105%   $238.7024   $238.70   $238.70   $238.70  
  Purchase #3 $58.92   7.762%   $63.4934   $63.49   $63.50   $63.50  
  Purchase #4 $164.42   8.721%   $178.7591   $178.76   $178.75   $178.80  
  Purchase #5 $33.60   8.645%   $36.5047   $36.50   $36.50   $36.50  
  Purchase #6 $217.33   11.202%   $241.6753   $241.68   $241.70   $241.70  
  Purchase #7 $103.30   7.791%   $111.3481   $111.35   $111.35   $111.30  
  7 purchase totals = $979.24       $1,065.7516   $1,065.75   $1,065.75   $1,065.80