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	$53.58	10.168%	$59.028	$59.03	$59.05	$59.00
Purchase #2	$159.93	13.531%	$181.5701	$181.57	$181.55	$181.60
Purchase #3	$64.50	4.452%	$67.3715	$67.37	$67.35	$67.40
Purchase #4	$122.69	9.806%	$134.721	$134.72	$134.70	$134.70
Purchase #5	$49.85	13.404%	$56.5319	$56.53	$56.55	$56.50
Purchase #6	$70.93	13.229%	$80.3133	$80.31	$80.30	$80.30
Purchase #7	$219.78	8.689%	$238.8767	$238.88	$238.90	$238.90
7 purchase totals =	$741.26		$818.4125	$818.41	$818.40	$818.40