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	$140.87	8.104%	$152.2861	$152.29	$152.30	$152.30
Purchase #2	$191.77	3.237%	$197.9776	$197.98	$198.00	$198.00
Purchase #3	$221.76	6.257%	$235.6355	$235.64	$235.65	$235.60
Purchase #4	$123.47	7.344%	$132.5376	$132.54	$132.55	$132.50
Purchase #5	$49.88	12.708%	$56.2188	$56.22	$56.20	$56.20
Purchase #6	$38.45	13.763%	$43.7419	$43.74	$43.75	$43.70
Purchase #7	$53.81	11.234%	$59.855	$59.86	$59.85	$59.90
7 purchase totals =	$820.01		$878.2525	$878.27	$878.30	$878.20