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	$46.44	13.490%	$52.7048	$52.70	$52.70	$52.70
Purchase #2	$45.80	6.231%	$48.6538	$48.65	$48.65	$48.70
Purchase #3	$65.62	7.779%	$70.7246	$70.72	$70.70	$70.70
Purchase #4	$177.61	10.433%	$196.1401	$196.14	$196.15	$196.10
Purchase #5	$35.54	7.818%	$38.3185	$38.32	$38.30	$38.30
Purchase #6	$194.76	11.845%	$217.8293	$217.83	$217.85	$217.80
Purchase #7	$243.38	13.498%	$276.2314	$276.23	$276.25	$276.20
7 purchase totals =	$809.15		$900.6025	$900.59	$900.60	$900.50