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 $212.88   13.382%   $241.3676   $241.37   $241.35   $241.40  
  Purchase #2 $187.35   4.377%   $195.5503   $195.55   $195.55   $195.60  
  Purchase #3 $16.25   12.573%   $18.2931   $18.29   $18.30   $18.30  
  Purchase #4 $71.40   4.668%   $74.733   $74.73   $74.75   $74.70  
  Purchase #5 $152.72   9.440%   $167.1368   $167.14   $167.15   $167.10  
  Purchase #6 $161.97   7.584%   $174.2538   $174.25   $174.25   $174.30  
  Purchase #7 $87.34   4.527%   $91.2939   $91.29   $91.30   $91.30  
  7 purchase totals = $889.91       $962.6285   $962.62   $962.65   $962.70