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 $206.61   7.848%   $222.8248   $222.82   $222.80   $222.80  
  Purchase #2 $176.57   9.286%   $192.9663   $192.97   $192.95   $193.00  
  Purchase #3 $164.59   6.318%   $174.9888   $174.99   $175.00   $175.00  
  Purchase #4 $61.84   9.166%   $67.5083   $67.51   $67.50   $67.50  
  Purchase #5 $221.69   11.865%   $247.9935   $247.99   $248.00   $248.00  
  Purchase #6 $117.50   4.265%   $122.5114   $122.51   $122.50   $122.50  
  Purchase #7 $192.48   5.186%   $202.462   $202.46   $202.45   $202.50  
  7 purchase totals = $1,141.28       $1,231.2551   $1,231.25   $1,231.20   $1,231.30