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	$244.73	12.609%	$275.588	$275.59	$275.60	$275.60
Purchase #2	$42.52	10.857%	$47.1364	$47.14	$47.15	$47.10
Purchase #3	$46.37	12.647%	$52.2344	$52.23	$52.25	$52.20
Purchase #4	$49.72	8.766%	$54.0785	$54.08	$54.10	$54.10
Purchase #5	$36.30	8.649%	$39.4396	$39.44	$39.45	$39.40
Purchase #6	$96.43	4.219%	$100.4984	$100.50	$100.50	$100.50
Purchase #7	$27.89	10.516%	$30.8229	$30.82	$30.80	$30.80
7 purchase totals =	$543.96		$599.7982	$599.80	$599.85	$599.70