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	$12.57	12.298%	$14.1159	$14.12	$14.10	$14.10
Purchase #2	$146.58	9.465%	$160.4538	$160.45	$160.45	$160.50
Purchase #3	$91.89	8.507%	$99.7071	$99.71	$99.70	$99.70
Purchase #4	$248.59	6.700%	$265.2455	$265.25	$265.25	$265.20
Purchase #5	$123.82	13.581%	$140.636	$140.64	$140.65	$140.60
Purchase #6	$107.33	3.434%	$111.0157	$111.02	$111.00	$111.00
Purchase #7	$10.35	3.631%	$10.7258	$10.73	$10.75	$10.70
7 purchase totals =	$741.13		$801.8998	$801.92	$801.90	$801.80