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	$54.69	5.355%	$57.6186	$57.62	$57.60	$57.60
Purchase #2	$246.32	12.853%	$277.9795	$277.98	$278.00	$278.00
Purchase #3	$130.49	10.589%	$144.3076	$144.31	$144.30	$144.30
Purchase #4	$152.63	8.162%	$165.0877	$165.09	$165.10	$165.10
Purchase #5	$59.90	12.623%	$67.4612	$67.46	$67.45	$67.50
Purchase #6	$6.58	9.378%	$7.1971	$7.20	$7.20	$7.20
Purchase #7	$15.86	4.705%	$16.6062	$16.61	$16.60	$16.60
7 purchase totals =	$666.47		$736.2579	$736.27	$736.25	$736.30