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	$19.42	5.508%	$20.4897	$20.49	$20.50	$20.50
Purchase #2	$173.91	12.717%	$196.0261	$196.03	$196.05	$196.00
Purchase #3	$200.34	5.181%	$210.7196	$210.72	$210.70	$210.70
Purchase #4	$150.55	7.677%	$162.1077	$162.11	$162.10	$162.10
Purchase #5	$185.92	13.575%	$211.1586	$211.16	$211.15	$211.20
Purchase #6	$138.79	4.690%	$145.2993	$145.30	$145.30	$145.30
Purchase #7	$120.56	11.670%	$134.6294	$134.63	$134.65	$134.60
7 purchase totals =	$989.49		$1,080.4304	$1,080.44	$1,080.45	$1,080.40