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	$79.39	12.703%	$89.4749	$89.47	$89.45	$89.50
Purchase #2	$75.54	8.753%	$82.152	$82.15	$82.15	$82.20
Purchase #3	$168.86	13.186%	$191.1259	$191.13	$191.15	$191.10
Purchase #4	$87.71	9.764%	$96.274	$96.27	$96.25	$96.30
Purchase #5	$17.84	4.373%	$18.6201	$18.62	$18.60	$18.60
Purchase #6	$231.35	6.808%	$247.1003	$247.10	$247.10	$247.10
Purchase #7	$47.45	7.821%	$51.1611	$51.16	$51.15	$51.20
7 purchase totals =	$708.14		$775.9083	$775.90	$775.85	$776.00