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 $169.58   13.393%   $192.2918   $192.29   $192.30   $192.30  
  Purchase #2 $241.82   3.502%   $250.2885   $250.29   $250.30   $250.30  
  Purchase #3 $31.86   13.143%   $36.0474   $36.05   $36.05   $36.00  
  Purchase #4 $228.54   4.594%   $239.0391   $239.04   $239.05   $239.00  
  Purchase #5 $154.43   11.743%   $172.5647   $172.56   $172.55   $172.60  
  Purchase #6 $237.63   10.771%   $263.2251   $263.23   $263.25   $263.20  
  Purchase #7 $96.69   7.138%   $103.5917   $103.59   $103.60   $103.60  
  7 purchase totals = $1,160.55       $1,257.0483   $1,257.05   $1,257.10   $1,257.00