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	$249.95	13.389%	$283.4158	$283.42	$283.40	$283.40
Purchase #2	$221.73	10.109%	$244.1447	$244.14	$244.15	$244.10
Purchase #3	$131.81	13.523%	$149.6347	$149.63	$149.65	$149.60
Purchase #4	$98.60	13.448%	$111.8597	$111.86	$111.85	$111.90
Purchase #5	$75.91	12.720%	$85.5658	$85.57	$85.55	$85.60
Purchase #6	$172.91	10.786%	$191.5601	$191.56	$191.55	$191.60
Purchase #7	$113.88	12.399%	$128	$128.00	$128.00	$128.00
7 purchase totals =	$1,064.79		$1,194.1808	$1,194.18	$1,194.15	$1,194.20