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	$134.59	6.484%	$143.3168	$143.32	$143.30	$143.30
Purchase #2	$129.82	10.105%	$142.9383	$142.94	$142.95	$142.90
Purchase #3	$143.83	4.182%	$149.845	$149.85	$149.85	$149.80
Purchase #4	$72.42	7.598%	$77.9225	$77.92	$77.90	$77.90
Purchase #5	$223.77	8.281%	$242.3004	$242.30	$242.30	$242.30
Purchase #6	$146.37	6.722%	$156.209	$156.21	$156.20	$156.20
Purchase #7	$172.31	3.791%	$178.8423	$178.84	$178.85	$178.80
7 purchase totals =	$1,023.11		$1,091.3743	$1,091.38	$1,091.35	$1,091.20