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	$14.35	3.515%	$14.8544	$14.85	$14.85	$14.90
Purchase #2	$215.80	5.851%	$228.4265	$228.43	$228.45	$228.40
Purchase #3	$180.31	8.792%	$196.1629	$196.16	$196.15	$196.20
Purchase #4	$165.87	7.479%	$178.2754	$178.28	$178.30	$178.30
Purchase #5	$71.84	10.594%	$79.4507	$79.45	$79.45	$79.50
Purchase #6	$49.80	11.309%	$55.4319	$55.43	$55.45	$55.40
Purchase #7	$220.74	5.735%	$233.3994	$233.40	$233.40	$233.40
7 purchase totals =	$918.71		$986.0012	$986.00	$986.05	$986.10