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	$221.62	9.301%	$242.2329	$242.23	$242.25	$242.20
Purchase #2	$84.30	6.821%	$90.0501	$90.05	$90.05	$90.10
Purchase #3	$176.80	5.147%	$185.8999	$185.90	$185.90	$185.90
Purchase #4	$166.63	10.481%	$184.0945	$184.09	$184.10	$184.10
Purchase #5	$184.52	6.247%	$196.047	$196.05	$196.05	$196.00
Purchase #6	$248.29	10.814%	$275.1401	$275.14	$275.15	$275.10
Purchase #7	$64.34	4.840%	$67.4541	$67.45	$67.45	$67.50
7 purchase totals =	$1,146.50		$1,240.9186	$1,240.91	$1,240.95	$1,240.90