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	$51.52	6.211%	$54.7199	$54.72	$54.70	$54.70
Purchase #2	$89.92	11.286%	$100.0684	$100.07	$100.05	$100.10
Purchase #3	$18.48	4.523%	$19.3159	$19.32	$19.30	$19.30
Purchase #4	$68.72	3.582%	$71.1816	$71.18	$71.20	$71.20
Purchase #5	$69.59	11.407%	$77.5281	$77.53	$77.55	$77.50
Purchase #6	$165.85	5.430%	$174.8557	$174.86	$174.85	$174.90
Purchase #7	$90.84	3.530%	$94.0467	$94.05	$94.05	$94.00
7 purchase totals =	$554.92		$591.7163	$591.73	$591.70	$591.70