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	$93.58	3.192%	$96.5671	$96.57	$96.55	$96.60
Purchase #2	$91.73	6.401%	$97.6016	$97.60	$97.60	$97.60
Purchase #3	$66.51	5.638%	$70.2598	$70.26	$70.25	$70.30
Purchase #4	$117.63	9.292%	$128.5602	$128.56	$128.55	$128.60
Purchase #5	$143.64	8.629%	$156.0347	$156.03	$156.05	$156.00
Purchase #6	$87.69	3.717%	$90.9494	$90.95	$90.95	$90.90
Purchase #7	$17.81	13.113%	$20.1454	$20.15	$20.15	$20.10
7 purchase totals =	$618.59		$660.1182	$660.12	$660.10	$660.10