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 $226.42   12.133%   $253.8915   $253.89   $253.90   $253.90  
  Purchase #2 $119.25   9.507%   $130.5871   $130.59   $130.60   $130.60  
  Purchase #3 $161.26   9.441%   $176.4846   $176.48   $176.50   $176.50  
  Purchase #4 $224.45   10.507%   $248.033   $248.03   $248.05   $248.00  
  Purchase #5 $87.30   12.441%   $98.161   $98.16   $98.15   $98.20  
  Purchase #6 $176.45   3.805%   $183.1639   $183.16   $183.15   $183.20  
  Purchase #7 $93.68   11.303%   $104.2687   $104.27   $104.25   $104.30  
  7 purchase totals = $1,088.81       $1,194.5898   $1,194.58   $1,194.60   $1,194.70