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	$72.41	10.717%	$80.1702	$80.17	$80.15	$80.20
Purchase #2	$142.31	10.824%	$157.7136	$157.71	$157.70	$157.70
Purchase #3	$176.49	13.738%	$200.7362	$200.74	$200.75	$200.70
Purchase #4	$20.51	6.769%	$21.8983	$21.90	$21.90	$21.90
Purchase #5	$86.87	3.361%	$89.7897	$89.79	$89.80	$89.80
Purchase #6	$50.94	13.301%	$57.7155	$57.72	$57.70	$57.70
Purchase #7	$99.50	10.710%	$110.1565	$110.16	$110.15	$110.20
7 purchase totals =	$649.03		$718.1800	$718.19	$718.15	$718.20