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	$133.45	13.835%	$151.9128	$151.91	$151.90	$151.90
Purchase #2	$210.49	3.648%	$218.1687	$218.17	$218.15	$218.20
Purchase #3	$107.68	3.394%	$111.3347	$111.33	$111.35	$111.30
Purchase #4	$143.47	5.701%	$151.6492	$151.65	$151.65	$151.60
Purchase #5	$39.84	13.384%	$45.1722	$45.17	$45.15	$45.20
Purchase #6	$128.33	10.128%	$141.3273	$141.33	$141.35	$141.30
Purchase #7	$14.39	4.278%	$15.0056	$15.01	$15.00	$15.00
7 purchase totals =	$777.65		$834.5705	$834.57	$834.55	$834.50