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	$236.85	5.322%	$249.4552	$249.46	$249.45	$249.50
Purchase #2	$151.59	10.708%	$167.8223	$167.82	$167.80	$167.80
Purchase #3	$30.86	13.522%	$35.0329	$35.03	$35.05	$35.00
Purchase #4	$49.53	10.467%	$54.7143	$54.71	$54.70	$54.70
Purchase #5	$250.76	11.153%	$278.7273	$278.73	$278.75	$278.70
Purchase #6	$106.39	7.804%	$114.6927	$114.69	$114.70	$114.70
Purchase #7	$91.47	8.646%	$99.3785	$99.38	$99.40	$99.40
7 purchase totals =	$917.45		$999.8232	$999.82	$999.85	$999.80