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	$102.89	3.558%	$106.5508	$106.55	$106.55	$106.60
Purchase #2	$241.86	10.646%	$267.6084	$267.61	$267.60	$267.60
Purchase #3	$191.69	4.213%	$199.7659	$199.77	$199.75	$199.80
Purchase #4	$48.83	6.672%	$52.0879	$52.09	$52.10	$52.10
Purchase #5	$23.32	11.135%	$25.9167	$25.92	$25.90	$25.90
Purchase #6	$69.55	10.749%	$77.0259	$77.03	$77.05	$77.00
Purchase #7	$54.92	9.111%	$59.9238	$59.92	$59.90	$59.90
7 purchase totals =	$733.06		$788.8794	$788.89	$788.85	$788.90