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	$38.70	5.751%	$40.9256	$40.93	$40.95	$40.90
Purchase #2	$22.50	11.857%	$25.1678	$25.17	$25.15	$25.20
Purchase #3	$136.92	5.621%	$144.6163	$144.62	$144.60	$144.60
Purchase #4	$90.25	10.631%	$99.8445	$99.84	$99.85	$99.80
Purchase #5	$45.69	4.580%	$47.7826	$47.78	$47.80	$47.80
Purchase #6	$224.84	7.136%	$240.8846	$240.88	$240.90	$240.90
Purchase #7	$124.75	5.780%	$131.9606	$131.96	$131.95	$132.00
7 purchase totals =	$683.65		$731.1820	$731.18	$731.20	$731.20