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	$246.42	7.683%	$265.3524	$265.35	$265.35	$265.40
Purchase #2	$73.56	10.466%	$81.2588	$81.26	$81.25	$81.30
Purchase #3	$80.76	4.347%	$84.2706	$84.27	$84.25	$84.30
Purchase #4	$134.45	3.729%	$139.4636	$139.46	$139.45	$139.50
Purchase #5	$56.65	9.298%	$61.9173	$61.92	$61.90	$61.90
Purchase #6	$63.85	13.745%	$72.6262	$72.63	$72.65	$72.60
Purchase #7	$89.39	11.187%	$99.3901	$99.39	$99.40	$99.40
7 purchase totals =	$745.08		$804.2790	$804.28	$804.25	$804.40