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	$205.82	8.265%	$222.831	$222.83	$222.85	$222.80
Purchase #2	$103.35	10.537%	$114.24	$114.24	$114.25	$114.20
Purchase #3	$72.64	12.168%	$81.4788	$81.48	$81.50	$81.50
Purchase #4	$199.47	13.148%	$225.6963	$225.70	$225.70	$225.70
Purchase #5	$38.69	4.556%	$40.4527	$40.45	$40.45	$40.50
Purchase #6	$83.70	6.453%	$89.1012	$89.10	$89.10	$89.10
Purchase #7	$143.91	3.715%	$149.2563	$149.26	$149.25	$149.30
7 purchase totals =	$847.58		$923.0563	$923.06	$923.10	$923.10