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	$47.77	11.758%	$53.3868	$53.39	$53.40	$53.40
Purchase #2	$56.74	8.630%	$61.6367	$61.64	$61.65	$61.60
Purchase #3	$228.67	11.612%	$255.2232	$255.22	$255.20	$255.20
Purchase #4	$32.59	8.157%	$35.2484	$35.25	$35.25	$35.20
Purchase #5	$204.78	12.271%	$229.9086	$229.91	$229.90	$229.90
Purchase #6	$75.79	4.421%	$79.1407	$79.14	$79.15	$79.10
Purchase #7	$163.57	13.432%	$185.5407	$185.54	$185.55	$185.50
7 purchase totals =	$809.91		$900.0851	$900.09	$900.10	$899.90