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	$196.95	12.667%	$221.8977	$221.90	$221.90	$221.90
Purchase #2	$49.29	11.257%	$54.8386	$54.84	$54.85	$54.80
Purchase #3	$79.73	13.682%	$90.6387	$90.64	$90.65	$90.60
Purchase #4	$202.43	9.810%	$222.2884	$222.29	$222.30	$222.30
Purchase #5	$76.40	7.665%	$82.2561	$82.26	$82.25	$82.30
Purchase #6	$42.28	12.782%	$47.6842	$47.68	$47.70	$47.70
Purchase #7	$112.28	13.436%	$127.3659	$127.37	$127.35	$127.40
7 purchase totals =	$759.36		$846.9696	$846.98	$847.00	$847.00