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 $239.54   11.443%   $266.9506   $266.95   $266.95   $267.00  
  Purchase #2 $230.38   10.370%   $254.2704   $254.27   $254.25   $254.30  
  Purchase #3 $71.28   5.260%   $75.0293   $75.03   $75.05   $75.00  
  Purchase #4 $228.93   11.398%   $255.0234   $255.02   $255.00   $255.00  
  Purchase #5 $117.29   8.556%   $127.3253   $127.33   $127.35   $127.30  
  Purchase #6 $220.44   4.768%   $230.9506   $230.95   $230.95   $231.00  
  Purchase #7 $33.91   3.511%   $35.1006   $35.10   $35.10   $35.10  
  7 purchase totals = $1,141.77       $1,244.6502   $1,244.65   $1,244.65   $1,244.70