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	$137.57	5.697%	$145.4074	$145.41	$145.40	$145.40
Purchase #2	$168.72	12.326%	$189.5164	$189.52	$189.50	$189.50
Purchase #3	$143.93	10.407%	$158.9088	$158.91	$158.90	$158.90
Purchase #4	$19.54	9.649%	$21.4254	$21.43	$21.45	$21.40
Purchase #5	$72.76	13.151%	$82.3287	$82.33	$82.35	$82.30
Purchase #6	$211.96	6.209%	$225.1206	$225.12	$225.10	$225.10
Purchase #7	$191.91	8.333%	$207.9019	$207.90	$207.90	$207.90
7 purchase totals =	$946.39		$1,030.6092	$1,030.62	$1,030.60	$1,030.50