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	$50.85	6.709%	$54.2615	$54.26	$54.25	$54.30
Purchase #2	$185.32	13.318%	$210.0009	$210.00	$210.00	$210.00
Purchase #3	$10.81	3.103%	$11.1454	$11.15	$11.15	$11.10
Purchase #4	$59.77	12.190%	$67.056	$67.06	$67.05	$67.10
Purchase #5	$6.82	9.367%	$7.4588	$7.46	$7.45	$7.50
Purchase #6	$109.92	12.564%	$123.7303	$123.73	$123.75	$123.70
Purchase #7	$31.79	7.228%	$34.0878	$34.09	$34.10	$34.10
7 purchase totals =	$455.28		$507.7407	$507.75	$507.75	$507.80