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 $215.75   11.699%   $240.9906   $240.99   $241.00   $241.00  
  Purchase #2 $31.63   13.380%   $35.8621   $35.86   $35.85   $35.90  
  Purchase #3 $228.64   6.300%   $243.0443   $243.04   $243.05   $243.00  
  Purchase #4 $166.83   11.712%   $186.3691   $186.37   $186.35   $186.40  
  Purchase #5 $22.57   12.139%   $25.3098   $25.31   $25.30   $25.30  
  Purchase #6 $193.70   10.489%   $214.0172   $214.02   $214.00   $214.00  
  Purchase #7 $209.83   11.784%   $234.5564   $234.56   $234.55   $234.60  
  7 purchase totals = $1,068.95       $1,180.1495   $1,180.15   $1,180.10   $1,180.20