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 $187.98   4.240%   $195.9504   $195.95   $195.95   $196.00  
  Purchase #2 $233.98   9.294%   $255.7261   $255.73   $255.75   $255.70  
  Purchase #3 $74.89   8.773%   $81.4601   $81.46   $81.45   $81.50  
  Purchase #4 $203.82   13.377%   $231.085   $231.09   $231.10   $231.10  
  Purchase #5 $156.39   12.820%   $176.4392   $176.44   $176.45   $176.40  
  Purchase #6 $238.68   10.571%   $263.9109   $263.91   $263.90   $263.90  
  Purchase #7 $68.44   3.246%   $70.6616   $70.66   $70.65   $70.70  
  7 purchase totals = $1,164.18       $1,275.2333   $1,275.24   $1,275.25   $1,275.30