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	$37.39	12.383%	$42.02	$42.02	$42.00	$42.00
Purchase #2	$59.41	11.812%	$66.4275	$66.43	$66.45	$66.40
Purchase #3	$211.28	9.253%	$230.8297	$230.83	$230.85	$230.80
Purchase #4	$121.52	3.192%	$125.3989	$125.40	$125.40	$125.40
Purchase #5	$51.35	9.782%	$56.3731	$56.37	$56.35	$56.40
Purchase #6	$176.59	11.271%	$196.4935	$196.49	$196.50	$196.50
Purchase #7	$139.37	3.867%	$144.7594	$144.76	$144.75	$144.80
7 purchase totals =	$796.91		$862.3021	$862.30	$862.30	$862.30