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	$191.78	4.375%	$200.1704	$200.17	$200.15	$200.20
Purchase #2	$214.29	6.828%	$228.9217	$228.92	$228.90	$228.90
Purchase #3	$102.37	7.272%	$109.8143	$109.81	$109.80	$109.80
Purchase #4	$159.93	7.711%	$172.2622	$172.26	$172.25	$172.30
Purchase #5	$90.39	3.563%	$93.6106	$93.61	$93.60	$93.60
Purchase #6	$98.26	10.713%	$108.7866	$108.79	$108.80	$108.80
Purchase #7	$41.98	4.447%	$43.8469	$43.85	$43.85	$43.80
7 purchase totals =	$899.00		$957.4127	$957.41	$957.35	$957.40