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	$238.45	5.624%	$251.8604	$251.86	$251.85	$251.90
Purchase #2	$94.67	10.830%	$104.9228	$104.92	$104.90	$104.90
Purchase #3	$107.92	10.421%	$119.1663	$119.17	$119.15	$119.20
Purchase #4	$100.42	10.618%	$111.0826	$111.08	$111.10	$111.10
Purchase #5	$137.73	3.291%	$142.2627	$142.26	$142.25	$142.30
Purchase #6	$205.89	11.413%	$229.3882	$229.39	$229.40	$229.40
Purchase #7	$168.35	7.107%	$180.3146	$180.31	$180.30	$180.30
7 purchase totals =	$1,053.43		$1,138.9976	$1,138.99	$1,138.95	$1,139.10