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	$30.33	10.353%	$33.4701	$33.47	$33.45	$33.50
Purchase #2	$116.98	11.188%	$130.0677	$130.07	$130.05	$130.10
Purchase #3	$175.28	11.732%	$195.8438	$195.84	$195.85	$195.80
Purchase #4	$163.28	6.211%	$173.4213	$173.42	$173.40	$173.40
Purchase #5	$38.34	10.371%	$42.3162	$42.32	$42.30	$42.30
Purchase #6	$54.52	9.370%	$59.6285	$59.63	$59.65	$59.60
Purchase #7	$51.70	12.855%	$58.346	$58.35	$58.35	$58.30
7 purchase totals =	$630.43		$693.0936	$693.10	$693.05	$693.00