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	$19.27	6.106%	$20.4466	$20.45	$20.45	$20.40
Purchase #2	$143.63	11.272%	$159.82	$159.82	$159.80	$159.80
Purchase #3	$156.77	10.249%	$172.8374	$172.84	$172.85	$172.80
Purchase #4	$91.58	5.110%	$96.2597	$96.26	$96.25	$96.30
Purchase #5	$29.64	11.547%	$33.0625	$33.06	$33.05	$33.10
Purchase #6	$245.58	6.329%	$261.1228	$261.12	$261.10	$261.10
Purchase #7	$240.65	7.320%	$258.2656	$258.27	$258.25	$258.30
7 purchase totals =	$927.12		$1,001.8146	$1,001.82	$1,001.75	$1,001.80