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	$245.91	4.286%	$256.4497	$256.45	$256.45	$256.40
Purchase #2	$52.86	3.114%	$54.5061	$54.51	$54.50	$54.50
Purchase #3	$218.92	12.111%	$245.4334	$245.43	$245.45	$245.40
Purchase #4	$57.56	12.668%	$64.8517	$64.85	$64.85	$64.90
Purchase #5	$183.28	13.537%	$208.0906	$208.09	$208.10	$208.10
Purchase #6	$54.78	5.418%	$57.748	$57.75	$57.75	$57.70
Purchase #7	$98.55	4.460%	$102.9453	$102.95	$102.95	$102.90
7 purchase totals =	$911.86		$990.0248	$990.03	$990.05	$989.90