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 $245.97   8.851%   $267.7408   $267.74   $267.75   $267.70  
  Purchase #2 $92.54   5.133%   $97.2901   $97.29   $97.30   $97.30  
  Purchase #3 $167.63   13.521%   $190.2953   $190.30   $190.30   $190.30  
  Purchase #4 $183.63   12.138%   $205.919   $205.92   $205.90   $205.90  
  Purchase #5 $7.79   5.192%   $8.1945   $8.19   $8.20   $8.20  
  Purchase #6 $218.40   7.316%   $234.3781   $234.38   $234.40   $234.40  
  Purchase #7 $82.61   9.699%   $90.6223   $90.62   $90.60   $90.60  
  7 purchase totals = $998.57       $1,094.4401   $1,094.44   $1,094.45   $1,094.40