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	$151.77	8.598%	$164.8192	$164.82	$164.80	$164.80
Purchase #2	$16.37	4.753%	$17.1481	$17.15	$17.15	$17.10
Purchase #3	$125.86	3.701%	$130.5181	$130.52	$130.50	$130.50
Purchase #4	$174.35	9.841%	$191.5078	$191.51	$191.50	$191.50
Purchase #5	$158.67	8.477%	$172.1205	$172.12	$172.10	$172.10
Purchase #6	$126.62	4.764%	$132.6522	$132.65	$132.65	$132.70
Purchase #7	$39.88	6.342%	$42.4092	$42.41	$42.40	$42.40
7 purchase totals =	$793.52		$851.1751	$851.18	$851.10	$851.10