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	$29.56	4.561%	$30.9082	$30.91	$30.90	$30.90
Purchase #2	$100.63	11.139%	$111.8392	$111.84	$111.85	$111.80
Purchase #3	$204.78	9.405%	$224.0396	$224.04	$224.05	$224.00
Purchase #4	$107.76	6.198%	$114.439	$114.44	$114.45	$114.40
Purchase #5	$92.93	8.675%	$100.9917	$100.99	$101.00	$101.00
Purchase #6	$177.81	10.546%	$196.5618	$196.56	$196.55	$196.60
Purchase #7	$204.31	11.454%	$227.7117	$227.71	$227.70	$227.70
7 purchase totals =	$917.78		$1,006.4912	$1,006.49	$1,006.50	$1,006.40