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 $207.99   9.183%   $227.0897   $227.09   $227.10   $227.10  
  Purchase #2 $156.52   4.184%   $163.0688   $163.07   $163.05   $163.10  
  Purchase #3 $114.84   3.661%   $119.0443   $119.04   $119.05   $119.00  
  Purchase #4 $216.31   5.739%   $228.724   $228.72   $228.70   $228.70  
  Purchase #5 $13.63   11.497%   $15.197   $15.20   $15.20   $15.20  
  Purchase #6 $188.93   5.670%   $199.6423   $199.64   $199.65   $199.60  
  Purchase #7 $230.73   6.578%   $245.9074   $245.91   $245.90   $245.90  
  7 purchase totals = $1,128.95       $1,198.6735   $1,198.67   $1,198.65   $1,198.60