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	$134.33	13.388%	$152.3141	$152.31	$152.30	$152.30
Purchase #2	$143.87	13.102%	$162.7198	$162.72	$162.70	$162.70
Purchase #3	$179.57	8.131%	$194.1708	$194.17	$194.15	$194.20
Purchase #4	$46.94	10.810%	$52.0142	$52.01	$52.00	$52.00
Purchase #5	$61.56	9.350%	$67.3159	$67.32	$67.30	$67.30
Purchase #6	$60.54	8.470%	$65.6677	$65.67	$65.65	$65.70
Purchase #7	$105.79	4.371%	$110.4141	$110.41	$110.40	$110.40
7 purchase totals =	$732.60		$804.6166	$804.61	$804.50	$804.60