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	$22.34	3.416%	$23.1031	$23.10	$23.10	$23.10
Purchase #2	$104.77	6.216%	$111.2825	$111.28	$111.30	$111.30
Purchase #3	$121.91	4.701%	$127.641	$127.64	$127.65	$127.60
Purchase #4	$36.90	7.244%	$39.573	$39.57	$39.55	$39.60
Purchase #5	$155.78	6.837%	$166.4307	$166.43	$166.45	$166.40
Purchase #6	$71.55	8.546%	$77.6647	$77.66	$77.65	$77.70
Purchase #7	$86.92	10.240%	$95.8206	$95.82	$95.80	$95.80
7 purchase totals =	$600.17		$641.5156	$641.50	$641.50	$641.50