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	$62.95	12.832%	$71.0277	$71.03	$71.05	$71.00
Purchase #2	$51.78	8.196%	$56.0239	$56.02	$56.00	$56.00
Purchase #3	$135.36	11.367%	$150.7464	$150.75	$150.75	$150.70
Purchase #4	$129.70	5.647%	$137.0242	$137.02	$137.00	$137.00
Purchase #5	$142.90	12.545%	$160.8268	$160.83	$160.85	$160.80
Purchase #6	$104.96	3.540%	$108.6756	$108.68	$108.70	$108.70
Purchase #7	$116.58	12.500%	$131.1525	$131.15	$131.15	$131.20
7 purchase totals =	$744.23		$815.4771	$815.48	$815.50	$815.40