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	$121.71	8.146%	$131.6245	$131.62	$131.60	$131.60
Purchase #2	$97.43	13.196%	$110.2869	$110.29	$110.30	$110.30
Purchase #3	$168.65	11.420%	$187.9098	$187.91	$187.90	$187.90
Purchase #4	$121.31	5.858%	$128.4163	$128.42	$128.40	$128.40
Purchase #5	$220.40	8.128%	$238.3141	$238.31	$238.30	$238.30
Purchase #6	$31.80	5.472%	$33.5401	$33.54	$33.55	$33.50
Purchase #7	$172.35	7.477%	$185.2366	$185.24	$185.25	$185.20
7 purchase totals =	$933.65		$1,015.3283	$1,015.33	$1,015.30	$1,015.20