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	$180.94	7.742%	$194.9484	$194.95	$194.95	$194.90
Purchase #2	$160.88	6.704%	$171.6654	$171.67	$171.65	$171.70
Purchase #3	$100.35	9.797%	$110.1813	$110.18	$110.20	$110.20
Purchase #4	$60.53	10.264%	$66.7428	$66.74	$66.75	$66.70
Purchase #5	$19.57	5.224%	$20.5923	$20.59	$20.60	$20.60
Purchase #6	$50.44	8.192%	$54.572	$54.57	$54.55	$54.60
Purchase #7	$19.60	4.407%	$20.4638	$20.46	$20.45	$20.50
7 purchase totals =	$592.31		$639.1660	$639.16	$639.15	$639.20