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 $204.81   9.166%   $223.5829   $223.58   $223.60   $223.60  
  Purchase #2 $167.76   13.764%   $190.8505   $190.85   $190.85   $190.90  
  Purchase #3 $35.35   12.416%   $39.7391   $39.74   $39.75   $39.70  
  Purchase #4 $86.87   12.779%   $97.9711   $97.97   $97.95   $98.00  
  Purchase #5 $57.63   5.673%   $60.8993   $60.90   $60.90   $60.90  
  Purchase #6 $241.50   3.126%   $249.0493   $249.05   $249.05   $249.00  
  Purchase #7 $248.96   5.279%   $262.1026   $262.10   $262.10   $262.10  
  7 purchase totals = $1,042.88       $1,124.1948   $1,124.19   $1,124.20   $1,124.20