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	$6.34	6.265%	$6.7372	$6.74	$6.75	$6.70
Purchase #2	$99.26	12.121%	$111.2913	$111.29	$111.30	$111.30
Purchase #3	$10.44	6.689%	$11.1383	$11.14	$11.15	$11.10
Purchase #4	$213.76	9.191%	$233.4067	$233.41	$233.40	$233.40
Purchase #5	$137.63	5.854%	$145.6869	$145.69	$145.70	$145.70
Purchase #6	$127.86	11.411%	$142.4501	$142.45	$142.45	$142.50
Purchase #7	$121.39	13.792%	$138.1321	$138.13	$138.15	$138.10
7 purchase totals =	$716.68		$788.8426	$788.85	$788.90	$788.80