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	$38.42	10.786%	$42.564	$42.56	$42.55	$42.60
Purchase #2	$187.90	13.608%	$213.4694	$213.47	$213.45	$213.50
Purchase #3	$36.86	9.160%	$40.2364	$40.24	$40.25	$40.20
Purchase #4	$95.89	4.869%	$100.5589	$100.56	$100.55	$100.60
Purchase #5	$202.60	13.679%	$230.3137	$230.31	$230.30	$230.30
Purchase #6	$242.55	3.175%	$250.251	$250.25	$250.25	$250.30
Purchase #7	$237.77	3.824%	$246.8623	$246.86	$246.85	$246.90
7 purchase totals =	$1,041.99		$1,124.2557	$1,124.25	$1,124.20	$1,124.40