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	$129.58	6.368%	$137.8317	$137.83	$137.85	$137.80
Purchase #2	$29.78	8.691%	$32.3682	$32.37	$32.35	$32.40
Purchase #3	$107.77	6.159%	$114.4076	$114.41	$114.40	$114.40
Purchase #4	$40.77	5.156%	$42.8721	$42.87	$42.85	$42.90
Purchase #5	$129.88	5.505%	$137.0299	$137.03	$137.05	$137.00
Purchase #6	$79.32	4.323%	$82.749	$82.75	$82.75	$82.70
Purchase #7	$91.26	12.428%	$102.6018	$102.60	$102.60	$102.60
7 purchase totals =	$608.36		$649.8603	$649.86	$649.85	$649.80