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	$250.83	10.560%	$277.3176	$277.32	$277.30	$277.30
Purchase #2	$230.78	8.510%	$250.4194	$250.42	$250.40	$250.40
Purchase #3	$22.76	11.655%	$25.4127	$25.41	$25.40	$25.40
Purchase #4	$66.39	10.333%	$73.2501	$73.25	$73.25	$73.30
Purchase #5	$79.72	8.605%	$86.5799	$86.58	$86.60	$86.60
Purchase #6	$37.72	6.552%	$40.1914	$40.19	$40.20	$40.20
Purchase #7	$80.82	7.549%	$86.9211	$86.92	$86.90	$86.90
7 purchase totals =	$769.02		$840.0922	$840.09	$840.05	$840.10