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	$45.88	9.623%	$50.295	$50.30	$50.30	$50.30
Purchase #2	$85.31	4.852%	$89.4492	$89.45	$89.45	$89.40
Purchase #3	$138.90	7.360%	$149.123	$149.12	$149.10	$149.10
Purchase #4	$250.77	12.743%	$282.7256	$282.73	$282.75	$282.70
Purchase #5	$89.36	12.838%	$100.832	$100.83	$100.85	$100.80
Purchase #6	$19.78	3.401%	$20.4527	$20.45	$20.45	$20.50
Purchase #7	$137.85	5.380%	$145.2663	$145.27	$145.25	$145.30
7 purchase totals =	$767.85		$838.1438	$838.15	$838.15	$838.10