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	$178.47	3.828%	$185.3018	$185.30	$185.30	$185.30
Purchase #2	$95.29	8.794%	$103.6698	$103.67	$103.65	$103.70
Purchase #3	$42.59	10.584%	$47.0977	$47.10	$47.10	$47.10
Purchase #4	$175.55	13.526%	$199.2949	$199.29	$199.30	$199.30
Purchase #5	$38.67	3.574%	$40.0521	$40.05	$40.05	$40.10
Purchase #6	$72.85	9.447%	$79.7321	$79.73	$79.75	$79.70
Purchase #7	$178.90	5.800%	$189.2762	$189.28	$189.30	$189.30
7 purchase totals =	$782.32		$844.4246	$844.42	$844.45	$844.50