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	$17.52	3.248%	$18.089	$18.09	$18.10	$18.10
Purchase #2	$171.98	8.404%	$186.4332	$186.43	$186.45	$186.40
Purchase #3	$230.59	9.184%	$251.7674	$251.77	$251.75	$251.80
Purchase #4	$159.41	3.718%	$165.3369	$165.34	$165.35	$165.30
Purchase #5	$25.66	8.690%	$27.8899	$27.89	$27.90	$27.90
Purchase #6	$144.72	4.635%	$151.4278	$151.43	$151.45	$151.40
Purchase #7	$90.99	9.590%	$99.7159	$99.72	$99.70	$99.70
7 purchase totals =	$840.87		$900.6601	$900.67	$900.70	$900.60