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 $143.93   12.526%   $161.9587   $161.96   $161.95   $162.00  
  Purchase #2 $228.74   7.566%   $246.0465   $246.05   $246.05   $246.00  
  Purchase #3 $119.56   3.769%   $124.0662   $124.07   $124.05   $124.10  
  Purchase #4 $241.27   4.667%   $252.5301   $252.53   $252.55   $252.50  
  Purchase #5 $180.91   5.675%   $191.1766   $191.18   $191.20   $191.20  
  Purchase #6 $188.37   11.560%   $210.1456   $210.15   $210.15   $210.10  
  Purchase #7 $116.87   12.548%   $131.5348   $131.53   $131.55   $131.50  
  7 purchase totals = $1,219.65       $1,317.4585   $1,317.47   $1,317.50   $1,317.40