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	$110.48	7.267%	$118.5086	$118.51	$118.50	$118.50
Purchase #2	$156.75	9.132%	$171.0644	$171.06	$171.05	$171.10
Purchase #3	$19.54	13.723%	$22.2215	$22.22	$22.20	$22.20
Purchase #4	$56.38	9.477%	$61.7231	$61.72	$61.70	$61.70
Purchase #5	$185.79	3.423%	$192.1496	$192.15	$192.15	$192.10
Purchase #6	$59.66	4.792%	$62.5189	$62.52	$62.50	$62.50
Purchase #7	$46.32	6.472%	$49.3178	$49.32	$49.30	$49.30
7 purchase totals =	$634.92		$677.5039	$677.50	$677.40	$677.40