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 $165.41   6.441%   $176.0641   $176.06   $176.05   $176.10  
  Purchase #2 $71.69   5.608%   $75.7104   $75.71   $75.70   $75.70  
  Purchase #3 $106.49   6.298%   $113.1967   $113.20   $113.20   $113.20  
  Purchase #4 $237.73   4.402%   $248.1949   $248.19   $248.20   $248.20  
  Purchase #5 $87.47   6.236%   $92.9246   $92.92   $92.90   $92.90  
  Purchase #6 $89.90   13.304%   $101.8603   $101.86   $101.85   $101.90  
  Purchase #7 $22.97   5.575%   $24.2506   $24.25   $24.25   $24.30  
  7 purchase totals = $781.66       $832.2016   $832.19   $832.15   $832.30