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	$71.63	9.716%	$78.5896	$78.59	$78.60	$78.60
Purchase #2	$219.25	11.379%	$244.1985	$244.20	$244.20	$244.20
Purchase #3	$54.87	9.200%	$59.918	$59.92	$59.90	$59.90
Purchase #4	$118.26	10.538%	$130.7222	$130.72	$130.70	$130.70
Purchase #5	$190.31	4.510%	$198.893	$198.89	$198.90	$198.90
Purchase #6	$19.53	4.482%	$20.4053	$20.41	$20.40	$20.40
Purchase #7	$85.31	4.772%	$89.381	$89.38	$89.40	$89.40
7 purchase totals =	$759.16		$822.1076	$822.11	$822.10	$822.10