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	$230.37	10.376%	$254.2732	$254.27	$254.25	$254.30
Purchase #2	$133.96	13.514%	$152.0634	$152.06	$152.05	$152.10
Purchase #3	$120.39	11.236%	$133.917	$133.92	$133.90	$133.90
Purchase #4	$127.89	7.423%	$137.3833	$137.38	$137.40	$137.40
Purchase #5	$148.93	5.146%	$156.5939	$156.59	$156.60	$156.60
Purchase #6	$219.60	3.497%	$227.2794	$227.28	$227.30	$227.30
Purchase #7	$159.98	12.574%	$180.0959	$180.10	$180.10	$180.10
7 purchase totals =	$1,141.12		$1,241.6061	$1,241.60	$1,241.60	$1,241.70