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	$98.65	10.381%	$108.8909	$108.89	$108.90	$108.90
Purchase #2	$99.39	13.506%	$112.8136	$112.81	$112.80	$112.80
Purchase #3	$159.63	10.747%	$176.7854	$176.79	$176.80	$176.80
Purchase #4	$120.65	3.382%	$124.7304	$124.73	$124.75	$124.70
Purchase #5	$57.92	6.104%	$61.4554	$61.46	$61.45	$61.50
Purchase #6	$75.87	3.125%	$78.2409	$78.24	$78.25	$78.20
Purchase #7	$136.47	7.189%	$146.2808	$146.28	$146.30	$146.30
7 purchase totals =	$748.58		$809.1974	$809.20	$809.25	$809.20