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	$247.36	12.808%	$279.0419	$279.04	$279.05	$279.00
Purchase #2	$38.82	11.363%	$43.2311	$43.23	$43.25	$43.20
Purchase #3	$126.86	6.281%	$134.8281	$134.83	$134.85	$134.80
Purchase #4	$50.57	3.783%	$52.4831	$52.48	$52.50	$52.50
Purchase #5	$201.40	4.114%	$209.6856	$209.69	$209.70	$209.70
Purchase #6	$107.51	3.283%	$111.0396	$111.04	$111.05	$111.00
Purchase #7	$133.51	9.701%	$146.4618	$146.46	$146.45	$146.50
7 purchase totals =	$906.03		$976.7712	$976.77	$976.85	$976.70