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	$155.90	6.190%	$165.5502	$165.55	$165.55	$165.60
Purchase #2	$102.86	8.492%	$111.5949	$111.59	$111.60	$111.60
Purchase #3	$19.76	11.538%	$22.0399	$22.04	$22.05	$22.00
Purchase #4	$113.43	11.189%	$126.1217	$126.12	$126.10	$126.10
Purchase #5	$109.56	5.769%	$115.8805	$115.88	$115.90	$115.90
Purchase #6	$86.96	4.377%	$90.7662	$90.77	$90.75	$90.80
Purchase #7	$228.56	9.497%	$250.2663	$250.27	$250.25	$250.30
7 purchase totals =	$817.03		$882.2197	$882.22	$882.20	$882.30