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	$174.87	8.618%	$189.9403	$189.94	$189.95	$189.90
Purchase #2	$248.91	13.358%	$282.1594	$282.16	$282.15	$282.20
Purchase #3	$93.60	3.227%	$96.6205	$96.62	$96.60	$96.60
Purchase #4	$205.47	10.497%	$227.0382	$227.04	$227.05	$227.00
Purchase #5	$47.79	5.779%	$50.5518	$50.55	$50.55	$50.60
Purchase #6	$106.63	4.746%	$111.6907	$111.69	$111.70	$111.70
Purchase #7	$124.87	5.296%	$131.4831	$131.48	$131.50	$131.50
7 purchase totals =	$1,002.14		$1,089.4840	$1,089.48	$1,089.50	$1,089.50