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	$83.67	8.290%	$90.6062	$90.61	$90.60	$90.60
Purchase #2	$204.94	11.376%	$228.254	$228.25	$228.25	$228.30
Purchase #3	$57.56	6.846%	$61.5006	$61.50	$61.50	$61.50
Purchase #4	$177.85	5.455%	$187.5517	$187.55	$187.55	$187.60
Purchase #5	$49.76	9.177%	$54.3265	$54.33	$54.35	$54.30
Purchase #6	$31.33	4.820%	$32.8401	$32.84	$32.85	$32.80
Purchase #7	$148.69	10.568%	$164.4036	$164.40	$164.40	$164.40
7 purchase totals =	$753.80		$819.4827	$819.48	$819.50	$819.50