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	$126.49	9.396%	$138.375	$138.38	$138.40	$138.40
Purchase #2	$175.39	9.228%	$191.575	$191.58	$191.60	$191.60
Purchase #3	$40.72	4.374%	$42.5011	$42.50	$42.50	$42.50
Purchase #4	$35.77	3.782%	$37.1228	$37.12	$37.10	$37.10
Purchase #5	$69.48	4.320%	$72.4815	$72.48	$72.50	$72.50
Purchase #6	$113.81	5.866%	$120.4861	$120.49	$120.50	$120.50
Purchase #7	$102.85	4.627%	$107.6089	$107.61	$107.60	$107.60
7 purchase totals =	$664.51		$710.1504	$710.16	$710.20	$710.20