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 $58.37   13.770%   $66.4075   $66.41   $66.40   $66.40  
  Purchase #2 $202.37   8.381%   $219.3306   $219.33   $219.35   $219.30  
  Purchase #3 $119.87   8.373%   $129.9067   $129.91   $129.90   $129.90  
  Purchase #4 $250.69   4.628%   $262.2919   $262.29   $262.30   $262.30  
  Purchase #5 $193.75   7.509%   $208.2987   $208.30   $208.30   $208.30  
  Purchase #6 $69.81   5.120%   $73.3843   $73.38   $73.40   $73.40  
  Purchase #7 $152.72   5.229%   $160.7057   $160.71   $160.70   $160.70  
  7 purchase totals = $1,047.58       $1,120.3254   $1,120.33   $1,120.35   $1,120.30