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	$161.95	6.490%	$172.4606	$172.46	$172.45	$172.50
Purchase #2	$85.29	4.627%	$89.2364	$89.24	$89.25	$89.20
Purchase #3	$48.33	12.133%	$54.1939	$54.19	$54.20	$54.20
Purchase #4	$94.35	9.562%	$103.3717	$103.37	$103.35	$103.40
Purchase #5	$35.53	12.344%	$39.9158	$39.92	$39.90	$39.90
Purchase #6	$64.41	12.828%	$72.6725	$72.67	$72.65	$72.70
Purchase #7	$5.80	5.773%	$6.1348	$6.13	$6.15	$6.10
7 purchase totals =	$495.66		$537.9857	$537.98	$537.95	$538.00