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	$245.37	8.116%	$265.2842	$265.28	$265.30	$265.30
Purchase #2	$218.45	7.389%	$234.5913	$234.59	$234.60	$234.60
Purchase #3	$54.28	9.667%	$59.5272	$59.53	$59.55	$59.50
Purchase #4	$41.34	13.158%	$46.7795	$46.78	$46.80	$46.80
Purchase #5	$150.70	6.600%	$160.6462	$160.65	$160.65	$160.60
Purchase #6	$25.58	6.692%	$27.2918	$27.29	$27.30	$27.30
Purchase #7	$175.70	8.200%	$190.1074	$190.11	$190.10	$190.10
7 purchase totals =	$911.42		$984.2276	$984.23	$984.30	$984.20