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 $102.63   10.617%   $113.5262   $113.53   $113.55   $113.50  
  Purchase #2 $198.65   11.563%   $221.6199   $221.62   $221.60   $221.60  
  Purchase #3 $49.90   5.170%   $52.4798   $52.48   $52.50   $52.50  
  Purchase #4 $195.99   4.702%   $205.2054   $205.21   $205.20   $205.20  
  Purchase #5 $206.62   4.237%   $215.3745   $215.37   $215.35   $215.40  
  Purchase #6 $45.33   5.375%   $47.7665   $47.77   $47.75   $47.80  
  Purchase #7 $87.53   9.106%   $95.5005   $95.50   $95.50   $95.50  
  7 purchase totals = $886.65       $951.4728   $951.48   $951.45   $951.50