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	$82.94	5.589%	$87.5755	$87.58	$87.60	$87.60
Purchase #2	$80.61	6.582%	$85.9158	$85.92	$85.90	$85.90
Purchase #3	$66.50	9.473%	$72.7995	$72.80	$72.80	$72.80
Purchase #4	$64.75	4.287%	$67.5258	$67.53	$67.55	$67.50
Purchase #5	$156.99	3.232%	$162.0639	$162.06	$162.05	$162.10
Purchase #6	$115.91	11.594%	$129.3486	$129.35	$129.35	$129.30
Purchase #7	$37.42	10.702%	$41.4247	$41.42	$41.40	$41.40
7 purchase totals =	$605.12		$646.6538	$646.66	$646.65	$646.60