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	$169.64	11.834%	$189.7152	$189.72	$189.70	$189.70
Purchase #2	$143.76	7.763%	$154.9201	$154.92	$154.90	$154.90
Purchase #3	$115.36	10.287%	$127.2271	$127.23	$127.25	$127.20
Purchase #4	$113.76	4.291%	$118.6414	$118.64	$118.65	$118.60
Purchase #5	$108.91	3.247%	$112.4463	$112.45	$112.45	$112.40
Purchase #6	$94.37	8.410%	$102.3065	$102.31	$102.30	$102.30
Purchase #7	$89.51	13.431%	$101.5321	$101.53	$101.55	$101.50
7 purchase totals =	$835.31		$906.7887	$906.80	$906.80	$906.60