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	$100.49	7.696%	$108.2237	$108.22	$108.20	$108.20
Purchase #2	$128.30	5.134%	$134.8869	$134.89	$134.90	$134.90
Purchase #3	$112.62	12.871%	$127.1153	$127.12	$127.10	$127.10
Purchase #4	$232.69	13.630%	$264.4056	$264.41	$264.40	$264.40
Purchase #5	$146.55	3.526%	$151.7174	$151.72	$151.70	$151.70
Purchase #6	$57.29	8.836%	$62.3521	$62.35	$62.35	$62.40
Purchase #7	$102.28	5.678%	$108.0875	$108.09	$108.10	$108.10
7 purchase totals =	$880.22		$956.7885	$956.80	$956.75	$956.80