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	$37.65	12.292%	$42.2779	$42.28	$42.30	$42.30
Purchase #2	$84.35	5.536%	$89.0196	$89.02	$89.00	$89.00
Purchase #3	$66.35	12.442%	$74.6053	$74.61	$74.60	$74.60
Purchase #4	$185.84	4.711%	$194.5949	$194.59	$194.60	$194.60
Purchase #5	$225.76	13.546%	$256.3414	$256.34	$256.35	$256.30
Purchase #6	$102.38	5.339%	$107.8461	$107.85	$107.85	$107.80
Purchase #7	$128.28	13.300%	$145.3412	$145.34	$145.35	$145.30
7 purchase totals =	$830.61		$910.0264	$910.03	$910.05	$909.90