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	$19.40	7.389%	$20.8335	$20.83	$20.85	$20.80
Purchase #2	$222.45	4.359%	$232.1466	$232.15	$232.15	$232.10
Purchase #3	$167.69	9.541%	$183.6893	$183.69	$183.70	$183.70
Purchase #4	$129.75	10.801%	$143.7643	$143.76	$143.75	$143.80
Purchase #5	$93.26	6.684%	$99.4935	$99.49	$99.50	$99.50
Purchase #6	$47.83	11.627%	$53.3912	$53.39	$53.40	$53.40
Purchase #7	$220.60	13.333%	$250.0126	$250.01	$250.00	$250.00
7 purchase totals =	$900.98		$983.3310	$983.32	$983.35	$983.30