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	$56.71	4.274%	$59.1338	$59.13	$59.15	$59.10
Purchase #2	$52.25	8.343%	$56.6092	$56.61	$56.60	$56.60
Purchase #3	$91.82	5.368%	$96.7489	$96.75	$96.75	$96.70
Purchase #4	$153.61	8.786%	$167.1062	$167.11	$167.10	$167.10
Purchase #5	$80.57	4.552%	$84.2375	$84.24	$84.25	$84.20
Purchase #6	$84.74	10.675%	$93.786	$93.79	$93.80	$93.80
Purchase #7	$127.52	11.860%	$142.6439	$142.64	$142.65	$142.60
7 purchase totals =	$647.22		$700.2655	$700.27	$700.30	$700.10