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	$6.80	13.377%	$7.7096	$7.71	$7.70	$7.70
Purchase #2	$78.43	7.787%	$84.5373	$84.54	$84.55	$84.50
Purchase #3	$55.63	7.458%	$59.7789	$59.78	$59.80	$59.80
Purchase #4	$68.77	13.653%	$78.1592	$78.16	$78.15	$78.20
Purchase #5	$112.89	10.580%	$124.8338	$124.83	$124.85	$124.80
Purchase #6	$75.44	3.708%	$78.2373	$78.24	$78.25	$78.20
Purchase #7	$8.65	7.586%	$9.3062	$9.31	$9.30	$9.30
7 purchase totals =	$406.61		$442.5623	$442.57	$442.60	$442.50