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	$35.27	6.213%	$37.4613	$37.46	$37.45	$37.50
Purchase #2	$205.45	8.523%	$222.9605	$222.96	$222.95	$223.00
Purchase #3	$71.67	3.401%	$74.1075	$74.11	$74.10	$74.10
Purchase #4	$52.69	3.873%	$54.7307	$54.73	$54.75	$54.70
Purchase #5	$66.30	6.617%	$70.6871	$70.69	$70.70	$70.70
Purchase #6	$67.61	5.286%	$71.1839	$71.18	$71.20	$71.20
Purchase #7	$22.32	9.633%	$24.4701	$24.47	$24.45	$24.50
7 purchase totals =	$521.31		$555.6011	$555.60	$555.60	$555.70