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	$163.99	12.120%	$183.8656	$183.87	$183.85	$183.90
Purchase #2	$139.93	12.397%	$157.2771	$157.28	$157.30	$157.30
Purchase #3	$98.65	11.283%	$109.7807	$109.78	$109.80	$109.80
Purchase #4	$19.43	10.687%	$21.5065	$21.51	$21.50	$21.50
Purchase #5	$77.91	9.121%	$85.0162	$85.02	$85.00	$85.00
Purchase #6	$63.90	11.602%	$71.3137	$71.31	$71.30	$71.30
Purchase #7	$48.48	5.495%	$51.144	$51.14	$51.15	$51.10
7 purchase totals =	$612.29		$679.9038	$679.91	$679.90	$679.90