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	$71.89	13.288%	$81.4427	$81.44	$81.45	$81.40
Purchase #2	$195.91	8.271%	$212.1137	$212.11	$212.10	$212.10
Purchase #3	$117.83	8.552%	$127.9068	$127.91	$127.90	$127.90
Purchase #4	$18.69	13.155%	$21.1487	$21.15	$21.15	$21.10
Purchase #5	$13.98	10.666%	$15.4711	$15.47	$15.45	$15.50
Purchase #6	$32.70	4.763%	$34.2575	$34.26	$34.25	$34.30
Purchase #7	$84.59	8.326%	$91.633	$91.63	$91.65	$91.60
7 purchase totals =	$535.59		$583.9735	$583.97	$583.95	$583.90