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 $66.98   6.836%   $71.5588   $71.56   $71.55   $71.60  
  Purchase #2 $91.38   4.870%   $95.8302   $95.83   $95.85   $95.80  
  Purchase #3 $111.78   5.716%   $118.1693   $118.17   $118.15   $118.20  
  Purchase #4 $213.49   6.551%   $227.4757   $227.48   $227.50   $227.50  
  Purchase #5 $228.77   10.612%   $253.0471   $253.05   $253.05   $253.00  
  Purchase #6 $148.56   4.193%   $154.7891   $154.79   $154.80   $154.80  
  Purchase #7 $215.99   10.697%   $239.0945   $239.09   $239.10   $239.10  
  7 purchase totals = $1,076.95       $1,159.9647   $1,159.97   $1,160.00   $1,160.00