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 $209.38   4.210%   $218.1949   $218.19   $218.20   $218.20  
  Purchase #2 $87.55   9.485%   $95.8541   $95.85   $95.85   $95.90  
  Purchase #3 $147.89   12.273%   $166.0405   $166.04   $166.05   $166.00  
  Purchase #4 $117.64   6.448%   $125.2254   $125.23   $125.25   $125.20  
  Purchase #5 $115.76   10.251%   $127.6266   $127.63   $127.65   $127.60  
  Purchase #6 $48.63   3.497%   $50.3306   $50.33   $50.35   $50.30  
  Purchase #7 $215.85   13.819%   $245.6783   $245.68   $245.70   $245.70  
  7 purchase totals = $942.70       $1,028.9504   $1,028.95   $1,029.05   $1,028.90