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	$47.47	5.166%	$49.9223	$49.92	$49.90	$49.90
Purchase #2	$214.65	3.823%	$222.8561	$222.86	$222.85	$222.90
Purchase #3	$248.26	10.298%	$273.8258	$273.83	$273.85	$273.80
Purchase #4	$144.32	9.558%	$158.1141	$158.11	$158.10	$158.10
Purchase #5	$118.42	11.841%	$132.4421	$132.44	$132.45	$132.40
Purchase #6	$89.69	9.644%	$98.3397	$98.34	$98.35	$98.30
Purchase #7	$237.90	6.360%	$253.0304	$253.03	$253.05	$253.00
7 purchase totals =	$1,100.71		$1,188.5305	$1,188.53	$1,188.55	$1,188.40