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 $37.48   9.712%   $41.1201   $41.12   $41.10   $41.10  
  Purchase #2 $41.53   13.280%   $47.0452   $47.05   $47.05   $47.00  
  Purchase #3 $183.38   6.284%   $194.9036   $194.90   $194.90   $194.90  
  Purchase #4 $171.53   10.318%   $189.2285   $189.23   $189.25   $189.20  
  Purchase #5 $241.41   8.757%   $262.5503   $262.55   $262.55   $262.60  
  Purchase #6 $189.92   5.152%   $199.7047   $199.70   $199.70   $199.70  
  Purchase #7 $37.65   7.474%   $40.464   $40.46   $40.45   $40.50  
  7 purchase totals = $902.90       $975.0164   $975.01   $975.00   $975.00