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	$134.32	4.106%	$139.8352	$139.84	$139.85	$139.80
Purchase #2	$54.95	12.264%	$61.6891	$61.69	$61.70	$61.70
Purchase #3	$57.29	13.525%	$65.0385	$65.04	$65.05	$65.00
Purchase #4	$157.26	13.473%	$178.4476	$178.45	$178.45	$178.40
Purchase #5	$51.32	5.762%	$54.2771	$54.28	$54.30	$54.30
Purchase #6	$55.34	12.631%	$62.33	$62.33	$62.35	$62.30
Purchase #7	$204.74	10.835%	$226.9236	$226.92	$226.90	$226.90
7 purchase totals =	$715.22		$788.5411	$788.55	$788.60	$788.40