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 $166.76   10.823%   $184.8084   $184.81   $184.80   $184.80  
  Purchase #2 $223.60   13.537%   $253.8687   $253.87   $253.85   $253.90  
  Purchase #3 $16.37   13.320%   $18.5505   $18.55   $18.55   $18.60  
  Purchase #4 $156.82   7.802%   $169.0551   $169.06   $169.05   $169.10  
  Purchase #5 $205.62   13.218%   $232.7989   $232.80   $232.80   $232.80  
  Purchase #6 $118.73   12.612%   $133.7042   $133.70   $133.70   $133.70  
  Purchase #7 $161.47   12.794%   $182.1285   $182.13   $182.15   $182.10  
  7 purchase totals = $1,049.37       $1,174.9143   $1,174.92   $1,174.90   $1,175.00