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 $124.55   8.575%   $135.2302   $135.23   $135.25   $135.20  
  Purchase #2 $180.63   8.865%   $196.6428   $196.64   $196.65   $196.60  
  Purchase #3 $176.68   8.692%   $192.037   $192.04   $192.05   $192.00  
  Purchase #4 $58.33   6.615%   $62.1885   $62.19   $62.20   $62.20  
  Purchase #5 $205.76   5.695%   $217.478   $217.48   $217.50   $217.50  
  Purchase #6 $218.35   9.642%   $239.4033   $239.40   $239.40   $239.40  
  Purchase #7 $218.78   4.278%   $228.1394   $228.14   $228.15   $228.10  
  7 purchase totals = $1,183.08       $1,271.1192   $1,271.12   $1,271.20   $1,271.00