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	$173.37	11.510%	$193.3249	$193.32	$193.30	$193.30
Purchase #2	$215.34	5.330%	$226.8176	$226.82	$226.80	$226.80
Purchase #3	$168.98	11.303%	$188.0798	$188.08	$188.10	$188.10
Purchase #4	$238.27	7.369%	$255.8281	$255.83	$255.85	$255.80
Purchase #5	$213.56	3.569%	$221.182	$221.18	$221.20	$221.20
Purchase #6	$224.60	13.337%	$254.5549	$254.55	$254.55	$254.60
Purchase #7	$78.57	13.388%	$89.089	$89.09	$89.10	$89.10
7 purchase totals =	$1,312.69		$1,428.8763	$1,428.87	$1,428.90	$1,428.90