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	$246.75	3.850%	$256.2499	$256.25	$256.25	$256.20
Purchase #2	$158.95	12.422%	$178.6948	$178.69	$178.70	$178.70
Purchase #3	$90.80	6.576%	$96.771	$96.77	$96.75	$96.80
Purchase #4	$94.38	9.233%	$103.0941	$103.09	$103.10	$103.10
Purchase #5	$94.96	7.326%	$101.9168	$101.92	$101.90	$101.90
Purchase #6	$71.90	10.464%	$79.4236	$79.42	$79.40	$79.40
Purchase #7	$235.79	12.170%	$264.4856	$264.49	$264.50	$264.50
7 purchase totals =	$993.53		$1,080.6358	$1,080.63	$1,080.60	$1,080.60