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	$243.48	11.822%	$272.2642	$272.26	$272.25	$272.30
Purchase #2	$151.57	13.129%	$171.4696	$171.47	$171.45	$171.50
Purchase #3	$115.59	5.715%	$122.196	$122.20	$122.20	$122.20
Purchase #4	$13.89	4.725%	$14.5463	$14.55	$14.55	$14.50
Purchase #5	$58.90	4.781%	$61.716	$61.72	$61.70	$61.70
Purchase #6	$103.26	10.846%	$114.4596	$114.46	$114.45	$114.50
Purchase #7	$103.32	5.111%	$108.6007	$108.60	$108.60	$108.60
7 purchase totals =	$790.01		$865.2524	$865.26	$865.20	$865.30