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	$238.38	10.763%	$264.0368	$264.04	$264.05	$264.00
Purchase #2	$103.49	6.118%	$109.8215	$109.82	$109.80	$109.80
Purchase #3	$90.27	3.605%	$93.5242	$93.52	$93.50	$93.50
Purchase #4	$12.40	8.601%	$13.4665	$13.47	$13.45	$13.50
Purchase #5	$124.61	10.529%	$137.7302	$137.73	$137.75	$137.70
Purchase #6	$32.43	3.485%	$33.5602	$33.56	$33.55	$33.60
Purchase #7	$74.68	10.124%	$82.2406	$82.24	$82.25	$82.20
7 purchase totals =	$676.26		$734.3800	$734.38	$734.35	$734.30