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	$232.40	11.700%	$259.5908	$259.59	$259.60	$259.60
Purchase #2	$141.87	12.153%	$159.1115	$159.11	$159.10	$159.10
Purchase #3	$51.45	6.718%	$54.9064	$54.91	$54.90	$54.90
Purchase #4	$114.96	13.729%	$130.7429	$130.74	$130.75	$130.70
Purchase #5	$47.57	9.222%	$51.9569	$51.96	$51.95	$52.00
Purchase #6	$91.84	9.480%	$100.5464	$100.55	$100.55	$100.50
Purchase #7	$17.86	9.683%	$19.5894	$19.59	$19.60	$19.60
7 purchase totals =	$697.95		$776.4443	$776.45	$776.45	$776.40