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	$109.30	13.428%	$123.9768	$123.98	$124.00	$124.00
Purchase #2	$86.85	6.810%	$92.7645	$92.76	$92.75	$92.80
Purchase #3	$195.26	3.193%	$201.4947	$201.49	$201.50	$201.50
Purchase #4	$64.59	9.837%	$70.9437	$70.94	$70.95	$70.90
Purchase #5	$118.26	7.787%	$127.4689	$127.47	$127.45	$127.50
Purchase #6	$229.94	10.622%	$254.3642	$254.36	$254.35	$254.40
Purchase #7	$95.83	10.183%	$105.5884	$105.59	$105.60	$105.60
7 purchase totals =	$900.03		$976.6012	$976.59	$976.60	$976.70