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	$32.44	6.244%	$34.4656	$34.47	$34.45	$34.50
Purchase #2	$170.63	4.865%	$178.9311	$178.93	$178.95	$178.90
Purchase #3	$79.40	13.754%	$90.3207	$90.32	$90.30	$90.30
Purchase #4	$131.34	7.279%	$140.9002	$140.90	$140.90	$140.90
Purchase #5	$72.56	13.836%	$82.5994	$82.60	$82.60	$82.60
Purchase #6	$130.26	12.196%	$146.1465	$146.15	$146.15	$146.10
Purchase #7	$60.40	3.261%	$62.3696	$62.37	$62.35	$62.40
7 purchase totals =	$677.03		$735.7331	$735.74	$735.70	$735.70