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	$227.28	9.306%	$248.4307	$248.43	$248.45	$248.40
Purchase #2	$98.55	13.409%	$111.7646	$111.76	$111.75	$111.80
Purchase #3	$162.90	5.308%	$171.5467	$171.55	$171.55	$171.50
Purchase #4	$173.85	8.859%	$189.2514	$189.25	$189.25	$189.30
Purchase #5	$167.91	4.763%	$175.9076	$175.91	$175.90	$175.90
Purchase #6	$171.72	5.845%	$181.757	$181.76	$181.75	$181.80
Purchase #7	$228.62	4.175%	$238.1649	$238.16	$238.15	$238.20
7 purchase totals =	$1,230.83		$1,316.8229	$1,316.82	$1,316.80	$1,316.90