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	$84.52	7.644%	$90.9807	$90.98	$91.00	$91.00
Purchase #2	$111.39	4.708%	$116.6342	$116.63	$116.65	$116.60
Purchase #3	$145.36	3.400%	$150.3022	$150.30	$150.30	$150.30
Purchase #4	$165.37	3.772%	$171.6078	$171.61	$171.60	$171.60
Purchase #5	$153.80	12.346%	$172.7881	$172.79	$172.80	$172.80
Purchase #6	$41.54	12.501%	$46.7329	$46.73	$46.75	$46.70
Purchase #7	$220.71	11.248%	$245.5355	$245.54	$245.55	$245.50
7 purchase totals =	$922.69		$994.5814	$994.58	$994.65	$994.50