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	$173.93	6.722%	$185.6216	$185.62	$185.60	$185.60
Purchase #2	$147.61	12.584%	$166.1852	$166.19	$166.20	$166.20
Purchase #3	$48.67	8.776%	$52.9413	$52.94	$52.95	$52.90
Purchase #4	$112.58	3.702%	$116.7477	$116.75	$116.75	$116.70
Purchase #5	$42.93	12.564%	$48.3237	$48.32	$48.30	$48.30
Purchase #6	$84.34	5.737%	$89.1786	$89.18	$89.20	$89.20
Purchase #7	$60.31	5.107%	$63.39	$63.39	$63.40	$63.40
7 purchase totals =	$670.37		$722.3881	$722.39	$722.40	$722.30