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	$241.28	3.490%	$249.7007	$249.70	$249.70	$249.70
Purchase #2	$100.35	6.468%	$106.8406	$106.84	$106.85	$106.80
Purchase #3	$193.35	13.103%	$218.6847	$218.68	$218.70	$218.70
Purchase #4	$109.34	3.743%	$113.4326	$113.43	$113.45	$113.40
Purchase #5	$52.89	13.175%	$59.8583	$59.86	$59.85	$59.90
Purchase #6	$101.35	6.655%	$108.0948	$108.09	$108.10	$108.10
Purchase #7	$213.83	13.511%	$242.7206	$242.72	$242.70	$242.70
7 purchase totals =	$1,012.39		$1,099.3323	$1,099.32	$1,099.35	$1,099.30