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 $182.68   8.514%   $198.2334   $198.23   $198.25   $198.20  
  Purchase #2 $222.41   5.204%   $233.9842   $233.98   $234.00   $234.00  
  Purchase #3 $185.41   4.353%   $193.4809   $193.48   $193.50   $193.50  
  Purchase #4 $25.86   12.253%   $29.0286   $29.03   $29.05   $29.00  
  Purchase #5 $234.84   10.285%   $258.9933   $258.99   $259.00   $259.00  
  Purchase #6 $167.53   13.679%   $190.4464   $190.45   $190.45   $190.40  
  Purchase #7 $92.76   4.614%   $97.0399   $97.04   $97.05   $97.00  
  7 purchase totals = $1,111.49       $1,201.2067   $1,201.20   $1,201.30   $1,201.10