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 $72.59   5.467%   $76.5585   $76.56   $76.55   $76.60  
  Purchase #2 $248.99   3.482%   $257.6598   $257.66   $257.65   $257.70  
  Purchase #3 $183.84   6.758%   $196.2639   $196.26   $196.25   $196.30  
  Purchase #4 $105.61   13.593%   $119.9656   $119.97   $119.95   $120.00  
  Purchase #5 $67.45   4.497%   $70.4832   $70.48   $70.50   $70.50  
  Purchase #6 $163.34   6.148%   $173.3821   $173.38   $173.40   $173.40  
  Purchase #7 $211.84   4.503%   $221.3792   $221.38   $221.40   $221.40  
  7 purchase totals = $1,053.66       $1,115.6923   $1,115.69   $1,115.70   $1,115.90