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	$46.72	8.514%	$50.6977	$50.70	$50.70	$50.70
Purchase #2	$94.31	5.841%	$99.8186	$99.82	$99.80	$99.80
Purchase #3	$54.34	7.194%	$58.2492	$58.25	$58.25	$58.20
Purchase #4	$89.36	3.319%	$92.3259	$92.33	$92.35	$92.30
Purchase #5	$100.82	10.319%	$111.2236	$111.22	$111.20	$111.20
Purchase #6	$139.90	13.549%	$158.8551	$158.86	$158.85	$158.90
Purchase #7	$141.52	6.757%	$151.0825	$151.08	$151.10	$151.10
7 purchase totals =	$666.97		$722.2526	$722.26	$722.25	$722.20