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	$139.48	11.179%	$155.0725	$155.07	$155.05	$155.10
Purchase #2	$149.87	8.451%	$162.5355	$162.54	$162.55	$162.50
Purchase #3	$37.30	9.466%	$40.8308	$40.83	$40.85	$40.80
Purchase #4	$110.32	12.749%	$124.3847	$124.38	$124.40	$124.40
Purchase #5	$246.42	8.457%	$267.2597	$267.26	$267.25	$267.30
Purchase #6	$145.53	11.858%	$162.7869	$162.79	$162.80	$162.80
Purchase #7	$18.92	8.646%	$20.5558	$20.56	$20.55	$20.60
7 purchase totals =	$847.84		$933.4259	$933.43	$933.45	$933.50