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	$10.60	13.271%	$12.0067	$12.01	$12.00	$12.00
Purchase #2	$189.94	10.740%	$210.3396	$210.34	$210.35	$210.30
Purchase #3	$161.95	6.551%	$172.5593	$172.56	$172.55	$172.60
Purchase #4	$201.43	7.403%	$216.3419	$216.34	$216.35	$216.30
Purchase #5	$134.55	8.109%	$145.4607	$145.46	$145.45	$145.50
Purchase #6	$131.60	10.743%	$145.7378	$145.74	$145.75	$145.70
Purchase #7	$106.79	4.451%	$111.5432	$111.54	$111.55	$111.50
7 purchase totals =	$936.86		$1,013.9892	$1,013.99	$1,014.00	$1,013.90