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	$133.32	7.399%	$143.1843	$143.18	$143.20	$143.20
Purchase #2	$203.46	8.739%	$221.2404	$221.24	$221.25	$221.20
Purchase #3	$16.98	7.445%	$18.2442	$18.24	$18.25	$18.20
Purchase #4	$97.91	9.430%	$107.1429	$107.14	$107.15	$107.10
Purchase #5	$77.81	10.280%	$85.8089	$85.81	$85.80	$85.80
Purchase #6	$47.72	11.318%	$53.1209	$53.12	$53.10	$53.10
Purchase #7	$36.57	6.251%	$38.856	$38.86	$38.85	$38.90
7 purchase totals =	$613.77		$667.5976	$667.59	$667.60	$667.50