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 $239.93   7.138%   $257.0562   $257.06   $257.05   $257.10  
  Purchase #2 $69.59   7.774%   $74.9999   $75.00   $75.00   $75.00  
  Purchase #3 $27.81   8.835%   $30.267   $30.27   $30.25   $30.30  
  Purchase #4 $216.53   11.395%   $241.2036   $241.20   $241.20   $241.20  
  Purchase #5 $195.72   8.113%   $211.5988   $211.60   $211.60   $211.60  
  Purchase #6 $180.53   8.664%   $196.1711   $196.17   $196.15   $196.20  
  Purchase #7 $44.95   5.130%   $47.2559   $47.26   $47.25   $47.30  
  7 purchase totals = $975.06       $1,058.5525   $1,058.56   $1,058.50   $1,058.70