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	$38.32	4.602%	$40.0835	$40.08	$40.10	$40.10
Purchase #2	$174.77	3.512%	$180.9079	$180.91	$180.90	$180.90
Purchase #3	$69.64	12.407%	$78.2802	$78.28	$78.30	$78.30
Purchase #4	$164.50	5.602%	$173.7153	$173.72	$173.70	$173.70
Purchase #5	$234.31	9.338%	$256.1899	$256.19	$256.20	$256.20
Purchase #6	$196.87	11.327%	$219.1695	$219.17	$219.15	$219.20
Purchase #7	$155.62	8.482%	$168.8197	$168.82	$168.80	$168.80
7 purchase totals =	$1,034.03		$1,117.1660	$1,117.17	$1,117.15	$1,117.20