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	$230.79	5.194%	$242.7772	$242.78	$242.80	$242.80
Purchase #2	$118.45	12.719%	$133.5157	$133.52	$133.50	$133.50
Purchase #3	$153.83	10.368%	$169.7791	$169.78	$169.80	$169.80
Purchase #4	$50.62	7.435%	$54.3836	$54.38	$54.40	$54.40
Purchase #5	$154.63	6.396%	$164.5201	$164.52	$164.50	$164.50
Purchase #6	$55.98	6.842%	$59.8102	$59.81	$59.80	$59.80
Purchase #7	$51.58	10.358%	$56.9227	$56.92	$56.90	$56.90
7 purchase totals =	$815.88		$881.7086	$881.71	$881.70	$881.70