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	$162.44	11.116%	$180.4968	$180.50	$180.50	$180.50
Purchase #2	$10.78	12.285%	$12.1043	$12.10	$12.10	$12.10
Purchase #3	$78.60	12.641%	$88.5358	$88.54	$88.55	$88.50
Purchase #4	$41.33	12.407%	$46.4578	$46.46	$46.45	$46.50
Purchase #5	$144.51	4.709%	$151.315	$151.32	$151.30	$151.30
Purchase #6	$120.61	13.731%	$137.171	$137.17	$137.15	$137.20
Purchase #7	$60.67	6.485%	$64.6044	$64.60	$64.60	$64.60
7 purchase totals =	$618.94		$680.6851	$680.69	$680.65	$680.70