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	$62.83	4.570%	$65.7013	$65.70	$65.70	$65.70
Purchase #2	$49.66	13.791%	$56.5086	$56.51	$56.50	$56.50
Purchase #3	$147.66	6.681%	$157.5252	$157.53	$157.55	$157.50
Purchase #4	$167.26	13.814%	$190.3653	$190.37	$190.35	$190.40
Purchase #5	$50.42	10.242%	$55.584	$55.58	$55.60	$55.60
Purchase #6	$159.83	9.444%	$174.9243	$174.92	$174.90	$174.90
Purchase #7	$127.91	13.832%	$145.6025	$145.60	$145.60	$145.60
7 purchase totals =	$765.57		$846.2112	$846.21	$846.20	$846.20