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 $208.79   6.830%   $223.0504   $223.05   $223.05   $223.10  
  Purchase #2 $95.55   6.106%   $101.3843   $101.38   $101.40   $101.40  
  Purchase #3 $93.93   12.792%   $105.9455   $105.95   $105.95   $105.90  
  Purchase #4 $163.53   7.158%   $175.2355   $175.24   $175.25   $175.20  
  Purchase #5 $229.65   10.454%   $253.6576   $253.66   $253.65   $253.70  
  Purchase #6 $200.38   6.305%   $213.014   $213.01   $213.00   $213.00  
  Purchase #7 $235.71   11.518%   $262.8591   $262.86   $262.85   $262.90  
  7 purchase totals = $1,227.54       $1,335.1464   $1,335.15   $1,335.15   $1,335.20