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	$203.54	12.405%	$228.7891	$228.79	$228.80	$228.80
Purchase #2	$18.79	12.837%	$21.2021	$21.20	$21.20	$21.20
Purchase #3	$240.67	9.503%	$263.5409	$263.54	$263.55	$263.50
Purchase #4	$33.68	4.490%	$35.1922	$35.19	$35.20	$35.20
Purchase #5	$16.28	13.832%	$18.5318	$18.53	$18.55	$18.50
Purchase #6	$222.53	7.143%	$238.4253	$238.43	$238.45	$238.40
Purchase #7	$152.39	13.470%	$172.9169	$172.92	$172.90	$172.90
7 purchase totals =	$887.88		$978.5983	$978.60	$978.65	$978.50