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	$51.75	6.663%	$55.1981	$55.20	$55.20	$55.20
Purchase #2	$159.77	12.253%	$179.3466	$179.35	$179.35	$179.30
Purchase #3	$34.52	7.513%	$37.1135	$37.11	$37.10	$37.10
Purchase #4	$21.51	8.665%	$23.3738	$23.37	$23.35	$23.40
Purchase #5	$48.40	13.795%	$55.0768	$55.08	$55.10	$55.10
Purchase #6	$142.56	5.650%	$150.6146	$150.61	$150.60	$150.60
Purchase #7	$61.50	5.217%	$64.7085	$64.71	$64.70	$64.70
7 purchase totals =	$520.01		$565.4319	$565.43	$565.40	$565.40