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	$129.28	7.564%	$139.0587	$139.06	$139.05	$139.10
Purchase #2	$207.33	12.452%	$233.1467	$233.15	$233.15	$233.10
Purchase #3	$77.34	6.732%	$82.5465	$82.55	$82.55	$82.50
Purchase #4	$142.83	8.764%	$155.3476	$155.35	$155.35	$155.30
Purchase #5	$233.93	6.140%	$248.2933	$248.29	$248.30	$248.30
Purchase #6	$228.28	4.734%	$239.0868	$239.09	$239.10	$239.10
Purchase #7	$95.60	7.573%	$102.8398	$102.84	$102.85	$102.80
7 purchase totals =	$1,114.59		$1,200.3194	$1,200.33	$1,200.35	$1,200.20