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	$53.71	5.313%	$56.5636	$56.56	$56.55	$56.60
Purchase #2	$179.25	11.873%	$200.5324	$200.53	$200.55	$200.50
Purchase #3	$216.49	10.126%	$238.4118	$238.41	$238.40	$238.40
Purchase #4	$34.64	8.859%	$37.7088	$37.71	$37.70	$37.70
Purchase #5	$32.43	3.585%	$33.5926	$33.59	$33.60	$33.60
Purchase #6	$235.71	13.242%	$266.9227	$266.92	$266.90	$266.90
Purchase #7	$73.85	5.375%	$77.8194	$77.82	$77.80	$77.80
7 purchase totals =	$826.08		$911.5513	$911.54	$911.50	$911.50