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	$134.62	13.394%	$152.651	$152.65	$152.65	$152.70
Purchase #2	$40.90	4.445%	$42.718	$42.72	$42.70	$42.70
Purchase #3	$96.69	12.243%	$108.5278	$108.53	$108.55	$108.50
Purchase #4	$64.60	4.403%	$67.4443	$67.44	$67.45	$67.40
Purchase #5	$18.98	6.769%	$20.2648	$20.26	$20.25	$20.30
Purchase #6	$174.91	7.313%	$187.7012	$187.70	$187.70	$187.70
Purchase #7	$11.68	5.297%	$12.2987	$12.30	$12.30	$12.30
7 purchase totals =	$542.38		$591.6058	$591.60	$591.60	$591.60