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 $91.64   7.200%   $98.2381   $98.24   $98.25   $98.20  
  Purchase #2 $146.88   10.264%   $161.9558   $161.96   $161.95   $162.00  
  Purchase #3 $96.88   6.730%   $103.4   $103.40   $103.40   $103.40  
  Purchase #4 $218.70   4.144%   $227.7629   $227.76   $227.75   $227.80  
  Purchase #5 $167.58   5.437%   $176.6913   $176.69   $176.70   $176.70  
  Purchase #6 $122.75   4.178%   $127.8785   $127.88   $127.90   $127.90  
  Purchase #7 $10.70   12.142%   $11.9992   $12.00   $12.00   $12.00  
  7 purchase totals = $855.13       $907.9258   $907.93   $907.95   $908.00