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	$139.91	4.517%	$146.2297	$146.23	$146.25	$146.20
Purchase #2	$92.31	10.665%	$102.1549	$102.15	$102.15	$102.20
Purchase #3	$29.87	12.326%	$33.5518	$33.55	$33.55	$33.60
Purchase #4	$233.53	4.497%	$244.0318	$244.03	$244.05	$244.00
Purchase #5	$142.25	11.364%	$158.4153	$158.42	$158.40	$158.40
Purchase #6	$228.70	10.635%	$253.0222	$253.02	$253.00	$253.00
Purchase #7	$59.58	4.201%	$62.083	$62.08	$62.10	$62.10
7 purchase totals =	$926.15		$999.4887	$999.48	$999.50	$999.50