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	$249.88	12.289%	$280.5878	$280.59	$280.60	$280.60
Purchase #2	$64.93	9.461%	$71.073	$71.07	$71.05	$71.10
Purchase #3	$90.90	7.417%	$97.6421	$97.64	$97.65	$97.60
Purchase #4	$64.88	11.482%	$72.3295	$72.33	$72.35	$72.30
Purchase #5	$93.52	6.767%	$99.8485	$99.85	$99.85	$99.80
Purchase #6	$156.53	4.408%	$163.4298	$163.43	$163.45	$163.40
Purchase #7	$15.81	9.568%	$17.3227	$17.32	$17.30	$17.30
7 purchase totals =	$736.45		$802.2334	$802.23	$802.25	$802.10