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 $199.60   12.622%   $224.7935   $224.79   $224.80   $224.80  
  Purchase #2 $84.85   10.794%   $94.0087   $94.01   $94.00   $94.00  
  Purchase #3 $233.81   8.762%   $254.2964   $254.30   $254.30   $254.30  
  Purchase #4 $157.35   6.503%   $167.5825   $167.58   $167.60   $167.60  
  Purchase #5 $118.84   4.386%   $124.0523   $124.05   $124.05   $124.10  
  Purchase #6 $187.84   9.651%   $205.9684   $205.97   $205.95   $206.00  
  Purchase #7 $248.36   13.765%   $282.5468   $282.55   $282.55   $282.50  
  7 purchase totals = $1,230.65       $1,353.2486   $1,353.25   $1,353.25   $1,353.30