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	$48.47	3.716%	$50.2711	$50.27	$50.25	$50.30
Purchase #2	$101.86	9.163%	$111.1934	$111.19	$111.20	$111.20
Purchase #3	$75.46	9.695%	$82.7758	$82.78	$82.80	$82.80
Purchase #4	$51.42	12.667%	$57.9334	$57.93	$57.95	$57.90
Purchase #5	$26.26	13.760%	$29.8734	$29.87	$29.85	$29.90
Purchase #6	$134.50	9.493%	$147.2681	$147.27	$147.25	$147.30
Purchase #7	$18.47	6.519%	$19.6741	$19.67	$19.65	$19.70
7 purchase totals =	$456.44		$498.9893	$498.98	$498.95	$499.10