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	$141.91	9.313%	$155.1261	$155.13	$155.15	$155.10
Purchase #2	$61.98	8.845%	$67.4621	$67.46	$67.45	$67.50
Purchase #3	$135.31	3.437%	$139.9606	$139.96	$139.95	$140.00
Purchase #4	$128.28	11.371%	$142.8667	$142.87	$142.85	$142.90
Purchase #5	$208.78	3.592%	$216.2794	$216.28	$216.30	$216.30
Purchase #6	$173.75	9.830%	$190.8296	$190.83	$190.85	$190.80
Purchase #7	$94.39	8.745%	$102.6444	$102.64	$102.65	$102.60
7 purchase totals =	$944.40		$1,015.1689	$1,015.17	$1,015.20	$1,015.20