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	$37.80	9.806%	$41.5067	$41.51	$41.50	$41.50
Purchase #2	$93.80	6.465%	$99.8642	$99.86	$99.85	$99.90
Purchase #3	$226.25	12.392%	$254.2869	$254.29	$254.30	$254.30
Purchase #4	$181.70	3.734%	$188.4847	$188.48	$188.50	$188.50
Purchase #5	$95.27	9.169%	$104.0053	$104.01	$104.00	$104.00
Purchase #6	$238.81	13.305%	$270.5837	$270.58	$270.60	$270.60
Purchase #7	$209.77	5.497%	$221.3011	$221.30	$221.30	$221.30
7 purchase totals =	$1,083.40		$1,180.0326	$1,180.03	$1,180.05	$1,180.10