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	$221.85	9.673%	$243.3096	$243.31	$243.30	$243.30
Purchase #2	$193.62	11.720%	$216.3123	$216.31	$216.30	$216.30
Purchase #3	$167.71	3.453%	$173.501	$173.50	$173.50	$173.50
Purchase #4	$9.72	12.204%	$10.9062	$10.91	$10.90	$10.90
Purchase #5	$7.25	9.384%	$7.9303	$7.93	$7.95	$7.90
Purchase #6	$138.89	3.401%	$143.6136	$143.61	$143.60	$143.60
Purchase #7	$117.86	7.145%	$126.2811	$126.28	$126.30	$126.30
7 purchase totals =	$856.90		$921.8541	$921.85	$921.85	$921.80