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	$238.91	7.289%	$256.3241	$256.32	$256.30	$256.30
Purchase #2	$196.83	4.681%	$206.0436	$206.04	$206.05	$206.00
Purchase #3	$105.62	12.270%	$118.5796	$118.58	$118.60	$118.60
Purchase #4	$159.46	12.737%	$179.7704	$179.77	$179.75	$179.80
Purchase #5	$156.46	10.127%	$172.3047	$172.30	$172.30	$172.30
Purchase #6	$42.83	5.427%	$45.1544	$45.15	$45.15	$45.20
Purchase #7	$98.96	6.795%	$105.6843	$105.68	$105.70	$105.70
7 purchase totals =	$999.07		$1,083.8611	$1,083.84	$1,083.85	$1,083.90