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	$226.46	8.228%	$245.0931	$245.09	$245.10	$245.10
Purchase #2	$6.82	4.133%	$7.1019	$7.10	$7.10	$7.10
Purchase #3	$100.87	6.558%	$107.4851	$107.49	$107.50	$107.50
Purchase #4	$100.88	8.618%	$109.5738	$109.57	$109.55	$109.60
Purchase #5	$9.91	6.165%	$10.521	$10.52	$10.50	$10.50
Purchase #6	$7.46	13.314%	$8.4532	$8.45	$8.45	$8.50
Purchase #7	$30.69	4.466%	$32.0606	$32.06	$32.05	$32.10
7 purchase totals =	$483.09		$520.2887	$520.28	$520.25	$520.40