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	$34.40	9.792%	$37.7684	$37.77	$37.75	$37.80
Purchase #2	$185.36	3.453%	$191.7605	$191.76	$191.75	$191.80
Purchase #3	$250.85	11.216%	$278.9853	$278.99	$279.00	$279.00
Purchase #4	$20.86	4.673%	$21.8348	$21.83	$21.85	$21.80
Purchase #5	$130.71	12.324%	$146.8187	$146.82	$146.80	$146.80
Purchase #6	$240.86	10.443%	$266.013	$266.01	$266.00	$266.00
Purchase #7	$34.43	3.717%	$35.7098	$35.71	$35.70	$35.70
7 purchase totals =	$897.47		$978.8905	$978.89	$978.85	$978.90