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 $42.89   7.720%   $46.2011   $46.20   $46.20   $46.20  
  Purchase #2 $225.31   6.186%   $239.2477   $239.25   $239.25   $239.20  
  Purchase #3 $124.77   6.551%   $132.9437   $132.94   $132.95   $132.90  
  Purchase #4 $67.54   9.698%   $74.09   $74.09   $74.10   $74.10  
  Purchase #5 $119.31   3.367%   $123.3272   $123.33   $123.35   $123.30  
  Purchase #6 $103.64   7.102%   $111.0005   $111.00   $111.00   $111.00  
  Purchase #7 $132.91   5.431%   $140.1283   $140.13   $140.15   $140.10  
  7 purchase totals = $816.37       $866.9385   $866.94   $867.00   $866.80