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 $144.65   11.618%   $161.4554   $161.46   $161.45   $161.50  
  Purchase #2 $45.42   9.838%   $49.8884   $49.89   $49.90   $49.90  
  Purchase #3 $248.78   10.297%   $274.3969   $274.40   $274.40   $274.40  
  Purchase #4 $146.97   13.799%   $167.2504   $167.25   $167.25   $167.30  
  Purchase #5 $182.48   7.377%   $195.9415   $195.94   $195.95   $195.90  
  Purchase #6 $59.41   13.226%   $67.2676   $67.27   $67.25   $67.30  
  Purchase #7 $101.94   5.323%   $107.3663   $107.37   $107.35   $107.40  
  7 purchase totals = $929.65       $1,023.5665   $1,023.58   $1,023.55   $1,023.70