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	$105.64	11.528%	$117.8182	$117.82	$117.80	$117.80
Purchase #2	$177.41	4.317%	$185.0688	$185.07	$185.05	$185.10
Purchase #3	$75.53	5.147%	$79.4175	$79.42	$79.40	$79.40
Purchase #4	$18.88	12.720%	$21.2815	$21.28	$21.30	$21.30
Purchase #5	$101.28	10.207%	$111.6176	$111.62	$111.60	$111.60
Purchase #6	$67.53	3.502%	$69.8949	$69.89	$69.90	$69.90
Purchase #7	$71.86	12.442%	$80.8008	$80.80	$80.80	$80.80
7 purchase totals =	$618.13		$665.8993	$665.90	$665.85	$665.90