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	$130.55	10.631%	$144.4288	$144.43	$144.45	$144.40
Purchase #2	$74.75	4.867%	$78.3881	$78.39	$78.40	$78.40
Purchase #3	$91.59	13.773%	$104.2047	$104.20	$104.20	$104.20
Purchase #4	$24.82	8.292%	$26.8781	$26.88	$26.90	$26.90
Purchase #5	$169.90	6.546%	$181.0217	$181.02	$181.00	$181.00
Purchase #6	$88.54	4.194%	$92.2534	$92.25	$92.25	$92.30
Purchase #7	$180.63	6.252%	$191.923	$191.92	$191.90	$191.90
7 purchase totals =	$760.78		$819.0978	$819.09	$819.10	$819.10