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	$171.49	4.279%	$178.8281	$178.83	$178.85	$178.80
Purchase #2	$167.64	13.325%	$189.978	$189.98	$190.00	$190.00
Purchase #3	$54.65	4.657%	$57.1951	$57.20	$57.20	$57.20
Purchase #4	$41.89	13.287%	$47.4559	$47.46	$47.45	$47.50
Purchase #5	$57.47	10.608%	$63.5664	$63.57	$63.55	$63.60
Purchase #6	$11.64	13.145%	$13.1701	$13.17	$13.15	$13.20
Purchase #7	$29.89	6.146%	$31.727	$31.73	$31.75	$31.70
7 purchase totals =	$534.67		$581.9206	$581.94	$581.95	$582.00