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	$122.94	4.421%	$128.3752	$128.38	$128.40	$128.40
Purchase #2	$133.82	8.460%	$145.1412	$145.14	$145.15	$145.10
Purchase #3	$89.51	11.287%	$99.613	$99.61	$99.60	$99.60
Purchase #4	$26.96	11.461%	$30.0499	$30.05	$30.05	$30.00
Purchase #5	$150.96	12.290%	$169.513	$169.51	$169.50	$169.50
Purchase #6	$143.78	4.645%	$150.4586	$150.46	$150.45	$150.50
Purchase #7	$110.97	9.688%	$121.7208	$121.72	$121.70	$121.70
7 purchase totals =	$778.94		$844.8717	$844.87	$844.85	$844.80