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	$34.80	13.131%	$39.3696	$39.37	$39.35	$39.40
Purchase #2	$37.69	11.818%	$42.1442	$42.14	$42.15	$42.10
Purchase #3	$225.60	5.869%	$238.8405	$238.84	$238.85	$238.80
Purchase #4	$91.72	12.772%	$103.4345	$103.43	$103.45	$103.40
Purchase #5	$90.55	11.281%	$100.7649	$100.76	$100.75	$100.80
Purchase #6	$219.97	7.740%	$236.9957	$237.00	$237.00	$237.00
Purchase #7	$5.83	7.680%	$6.2777	$6.28	$6.30	$6.30
7 purchase totals =	$706.16		$767.8271	$767.82	$767.85	$767.80