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	$42.81	6.832%	$45.7348	$45.73	$45.75	$45.70
Purchase #2	$90.75	4.313%	$94.664	$94.66	$94.65	$94.70
Purchase #3	$191.46	13.233%	$216.7959	$216.80	$216.80	$216.80
Purchase #4	$71.87	11.758%	$80.3205	$80.32	$80.30	$80.30
Purchase #5	$37.42	6.608%	$39.8927	$39.89	$39.90	$39.90
Purchase #6	$34.69	4.434%	$36.2282	$36.23	$36.25	$36.20
Purchase #7	$230.51	6.553%	$245.6153	$245.62	$245.60	$245.60
7 purchase totals =	$699.51		$759.2514	$759.25	$759.25	$759.20