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 $204.58   8.213%   $221.3822   $221.38   $221.40   $221.40  
  Purchase #2 $83.80   13.531%   $95.139   $95.14   $95.15   $95.10  
  Purchase #3 $136.44   13.465%   $154.8116   $154.81   $154.80   $154.80  
  Purchase #4 $61.33   13.121%   $69.3771   $69.38   $69.40   $69.40  
  Purchase #5 $217.92   3.587%   $225.7368   $225.74   $225.75   $225.70  
  Purchase #6 $111.70   6.194%   $118.6187   $118.62   $118.60   $118.60  
  Purchase #7 $192.64   13.306%   $218.2727   $218.27   $218.25   $218.30  
  7 purchase totals = $1,008.41       $1,103.3381   $1,103.34   $1,103.35   $1,103.30