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	$49.52	13.420%	$56.1656	$56.17	$56.15	$56.20
Purchase #2	$109.81	9.862%	$120.6395	$120.64	$120.65	$120.60
Purchase #3	$82.31	8.603%	$89.3911	$89.39	$89.40	$89.40
Purchase #4	$62.41	4.543%	$65.2453	$65.25	$65.25	$65.20
Purchase #5	$173.51	7.383%	$186.3202	$186.32	$186.30	$186.30
Purchase #6	$80.65	10.336%	$88.986	$88.99	$89.00	$89.00
Purchase #7	$149.77	7.313%	$160.7227	$160.72	$160.70	$160.70
7 purchase totals =	$707.98		$767.4704	$767.48	$767.45	$767.40