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	$54.71	5.623%	$57.7863	$57.79	$57.80	$57.80
Purchase #2	$236.47	8.143%	$255.7258	$255.73	$255.75	$255.70
Purchase #3	$232.90	9.279%	$254.5108	$254.51	$254.50	$254.50
Purchase #4	$235.52	6.195%	$250.1105	$250.11	$250.10	$250.10
Purchase #5	$212.52	12.283%	$238.6238	$238.62	$238.60	$238.60
Purchase #6	$158.76	8.626%	$172.4546	$172.45	$172.45	$172.50
Purchase #7	$213.56	7.859%	$230.3437	$230.34	$230.35	$230.30
7 purchase totals =	$1,344.44		$1,459.5555	$1,459.55	$1,459.55	$1,459.50