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 $213.82   13.300%   $242.2581   $242.26   $242.25   $242.30  
  Purchase #2 $208.61   12.721%   $235.1473   $235.15   $235.15   $235.10  
  Purchase #3 $91.95   4.561%   $96.1438   $96.14   $96.15   $96.10  
  Purchase #4 $171.75   9.227%   $187.5974   $187.60   $187.60   $187.60  
  Purchase #5 $243.38   8.375%   $263.7631   $263.76   $263.75   $263.80  
  Purchase #6 $183.97   4.554%   $192.348   $192.35   $192.35   $192.30  
  Purchase #7 $29.66   3.430%   $30.6773   $30.68   $30.70   $30.70  
  7 purchase totals = $1,143.14       $1,247.9350   $1,247.94   $1,247.95   $1,247.90