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	$171.78	10.379%	$189.609	$189.61	$189.60	$189.60
Purchase #2	$86.89	4.106%	$90.4577	$90.46	$90.45	$90.50
Purchase #3	$140.97	6.393%	$149.9822	$149.98	$150.00	$150.00
Purchase #4	$125.45	8.631%	$136.2776	$136.28	$136.30	$136.30
Purchase #5	$240.68	6.804%	$257.0559	$257.06	$257.05	$257.10
Purchase #6	$88.52	12.647%	$99.7151	$99.72	$99.70	$99.70
Purchase #7	$73.97	3.236%	$76.3637	$76.36	$76.35	$76.40
7 purchase totals =	$928.26		$999.4612	$999.47	$999.45	$999.60