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	$132.65	11.132%	$147.4166	$147.42	$147.40	$147.40
Purchase #2	$155.41	8.175%	$168.1148	$168.11	$168.10	$168.10
Purchase #3	$103.29	7.492%	$111.0285	$111.03	$111.05	$111.00
Purchase #4	$138.43	7.542%	$148.8704	$148.87	$148.85	$148.90
Purchase #5	$196.58	11.857%	$219.8885	$219.89	$219.90	$219.90
Purchase #6	$105.90	13.292%	$119.9762	$119.98	$120.00	$120.00
Purchase #7	$63.70	12.434%	$71.6205	$71.62	$71.60	$71.60
7 purchase totals =	$895.96		$986.9155	$986.92	$986.90	$986.90