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	$40.47	7.824%	$43.6364	$43.64	$43.65	$43.60
Purchase #2	$98.72	7.450%	$106.0746	$106.07	$106.05	$106.10
Purchase #3	$206.57	12.513%	$232.4181	$232.42	$232.40	$232.40
Purchase #4	$33.62	10.400%	$37.1165	$37.12	$37.10	$37.10
Purchase #5	$11.60	13.335%	$13.1469	$13.15	$13.15	$13.10
Purchase #6	$95.65	5.314%	$100.7328	$100.73	$100.75	$100.70
Purchase #7	$76.68	13.145%	$86.7596	$86.76	$86.75	$86.80
7 purchase totals =	$563.31		$619.8849	$619.89	$619.85	$619.80