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	$128.56	11.471%	$143.3071	$143.31	$143.30	$143.30
Purchase #2	$129.68	12.175%	$145.4685	$145.47	$145.45	$145.50
Purchase #3	$34.72	8.309%	$37.6049	$37.60	$37.60	$37.60
Purchase #4	$174.98	7.109%	$187.4193	$187.42	$187.40	$187.40
Purchase #5	$132.39	13.311%	$150.0124	$150.01	$150.00	$150.00
Purchase #6	$13.54	11.253%	$15.0637	$15.06	$15.05	$15.10
Purchase #7	$132.96	8.562%	$144.344	$144.34	$144.35	$144.30
7 purchase totals =	$746.83		$823.2199	$823.21	$823.15	$823.20