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	$210.52	10.402%	$232.4183	$232.42	$232.40	$232.40
Purchase #2	$80.64	12.258%	$90.5249	$90.52	$90.50	$90.50
Purchase #3	$81.60	4.560%	$85.321	$85.32	$85.30	$85.30
Purchase #4	$78.28	4.206%	$81.5725	$81.57	$81.55	$81.60
Purchase #5	$152.83	7.645%	$164.5139	$164.51	$164.50	$164.50
Purchase #6	$36.54	9.583%	$40.0416	$40.04	$40.05	$40.00
Purchase #7	$95.70	6.225%	$101.6573	$101.66	$101.65	$101.70
7 purchase totals =	$736.11		$796.0495	$796.04	$795.95	$796.00