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	$145.31	6.735%	$155.0966	$155.10	$155.10	$155.10
Purchase #2	$35.90	9.295%	$39.2369	$39.24	$39.25	$39.20
Purchase #3	$124.30	6.175%	$131.9755	$131.98	$132.00	$132.00
Purchase #4	$85.65	5.156%	$90.0661	$90.07	$90.05	$90.10
Purchase #5	$196.71	13.710%	$223.6789	$223.68	$223.70	$223.70
Purchase #6	$160.87	7.166%	$172.3979	$172.40	$172.40	$172.40
Purchase #7	$140.80	12.868%	$158.9181	$158.92	$158.90	$158.90
7 purchase totals =	$889.54		$971.3700	$971.39	$971.40	$971.40