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	$36.51	10.436%	$40.3202	$40.32	$40.30	$40.30
Purchase #2	$72.99	6.236%	$77.5417	$77.54	$77.55	$77.50
Purchase #3	$54.95	11.778%	$61.422	$61.42	$61.40	$61.40
Purchase #4	$44.44	11.162%	$49.4004	$49.40	$49.40	$49.40
Purchase #5	$74.38	4.185%	$77.4928	$77.49	$77.50	$77.50
Purchase #6	$136.77	6.624%	$145.8296	$145.83	$145.85	$145.80
Purchase #7	$191.79	10.153%	$211.2624	$211.26	$211.25	$211.30
7 purchase totals =	$611.83		$663.2691	$663.26	$663.25	$663.20