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	$29.91	5.333%	$31.5051	$31.51	$31.50	$31.50
Purchase #2	$61.61	9.246%	$67.3065	$67.31	$67.30	$67.30
Purchase #3	$77.95	3.559%	$80.7242	$80.72	$80.70	$80.70
Purchase #4	$192.57	6.127%	$204.3688	$204.37	$204.35	$204.40
Purchase #5	$58.88	5.390%	$62.0536	$62.05	$62.05	$62.10
Purchase #6	$166.25	11.501%	$185.3704	$185.37	$185.35	$185.40
Purchase #7	$61.27	6.167%	$65.0485	$65.05	$65.05	$65.00
7 purchase totals =	$648.44		$696.3771	$696.38	$696.30	$696.40