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 $231.71   7.421%   $248.9052   $248.91   $248.90   $248.90  
  Purchase #2 $116.77   11.539%   $130.2441   $130.24   $130.25   $130.20  
  Purchase #3 $30.95   10.577%   $34.2236   $34.22   $34.20   $34.20  
  Purchase #4 $69.86   5.813%   $73.921   $73.92   $73.90   $73.90  
  Purchase #5 $241.98   5.327%   $254.8703   $254.87   $254.85   $254.90  
  Purchase #6 $147.40   13.627%   $167.4862   $167.49   $167.50   $167.50  
  Purchase #7 $85.43   13.120%   $96.6384   $96.64   $96.65   $96.60  
  7 purchase totals = $924.10       $1,006.2888   $1,006.29   $1,006.25   $1,006.20