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	$18.56	12.863%	$20.9474	$20.95	$20.95	$20.90
Purchase #2	$53.55	7.827%	$57.7414	$57.74	$57.75	$57.70
Purchase #3	$74.56	5.365%	$78.5601	$78.56	$78.55	$78.60
Purchase #4	$249.80	3.707%	$259.0601	$259.06	$259.05	$259.10
Purchase #5	$49.59	13.526%	$56.2975	$56.30	$56.30	$56.30
Purchase #6	$110.41	11.829%	$123.4704	$123.47	$123.45	$123.50
Purchase #7	$25.51	13.547%	$28.9658	$28.97	$28.95	$29.00
7 purchase totals =	$581.98		$625.0427	$625.05	$625.00	$625.10