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 $169.91   6.846%   $181.542   $181.54   $181.55   $181.50  
  Purchase #2 $248.86   7.833%   $268.3532   $268.35   $268.35   $268.40  
  Purchase #3 $164.35   4.744%   $172.1468   $172.15   $172.15   $172.10  
  Purchase #4 $231.49   3.302%   $239.1338   $239.13   $239.15   $239.10  
  Purchase #5 $101.81   7.306%   $109.2482   $109.25   $109.25   $109.20  
  Purchase #6 $174.96   10.618%   $193.5373   $193.54   $193.55   $193.50  
  Purchase #7 $208.53   6.417%   $221.9114   $221.91   $221.90   $221.90  
  7 purchase totals = $1,299.91       $1,385.8727   $1,385.87   $1,385.90   $1,385.70