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	$135.71	11.740%	$151.6424	$151.64	$151.65	$151.60
Purchase #2	$51.60	3.256%	$53.2801	$53.28	$53.30	$53.30
Purchase #3	$78.28	13.241%	$88.6451	$88.65	$88.65	$88.60
Purchase #4	$105.60	5.852%	$111.7797	$111.78	$111.80	$111.80
Purchase #5	$15.39	3.275%	$15.894	$15.89	$15.90	$15.90
Purchase #6	$83.40	3.478%	$86.3007	$86.30	$86.30	$86.30
Purchase #7	$29.86	10.110%	$32.8788	$32.88	$32.90	$32.90
7 purchase totals =	$499.84		$540.4208	$540.42	$540.50	$540.40