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	$19.79	5.547%	$20.8878	$20.89	$20.90	$20.90
Purchase #2	$239.66	11.656%	$267.5948	$267.59	$267.60	$267.60
Purchase #3	$124.67	3.352%	$128.8489	$128.85	$128.85	$128.80
Purchase #4	$120.89	6.576%	$128.8397	$128.84	$128.85	$128.80
Purchase #5	$236.76	6.378%	$251.8606	$251.86	$251.85	$251.90
Purchase #6	$114.95	11.204%	$127.829	$127.83	$127.85	$127.80
Purchase #7	$6.68	8.179%	$7.2264	$7.23	$7.25	$7.20
7 purchase totals =	$863.40		$933.0872	$933.09	$933.15	$933.00