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	$56.93	13.143%	$64.4123	$64.41	$64.40	$64.40
Purchase #2	$190.83	4.538%	$199.4899	$199.49	$199.50	$199.50
Purchase #3	$134.80	5.817%	$142.6413	$142.64	$142.65	$142.60
Purchase #4	$16.78	11.822%	$18.7637	$18.76	$18.75	$18.80
Purchase #5	$41.56	8.450%	$45.0718	$45.07	$45.05	$45.10
Purchase #6	$79.66	4.561%	$83.2933	$83.29	$83.30	$83.30
Purchase #7	$178.95	3.431%	$185.0898	$185.09	$185.10	$185.10
7 purchase totals =	$699.51		$738.7621	$738.75	$738.75	$738.80