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	$140.34	13.834%	$159.7546	$159.75	$159.75	$159.80
Purchase #2	$175.44	8.125%	$189.6945	$189.69	$189.70	$189.70
Purchase #3	$233.75	3.467%	$241.8541	$241.85	$241.85	$241.90
Purchase #4	$96.93	7.222%	$103.9303	$103.93	$103.95	$103.90
Purchase #5	$120.72	11.247%	$134.2974	$134.30	$134.30	$134.30
Purchase #6	$98.81	12.458%	$111.1197	$111.12	$111.10	$111.10
Purchase #7	$142.79	3.377%	$147.612	$147.61	$147.60	$147.60
7 purchase totals =	$1,008.78		$1,088.2626	$1,088.25	$1,088.25	$1,088.30