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	$138.58	5.475%	$146.1673	$146.17	$146.15	$146.20
Purchase #2	$228.98	10.853%	$253.8312	$253.83	$253.85	$253.80
Purchase #3	$76.80	7.564%	$82.6092	$82.61	$82.60	$82.60
Purchase #4	$26.38	7.339%	$28.316	$28.32	$28.30	$28.30
Purchase #5	$121.31	5.759%	$128.2962	$128.30	$128.30	$128.30
Purchase #6	$35.56	10.762%	$39.387	$39.39	$39.40	$39.40
Purchase #7	$88.47	8.409%	$95.9094	$95.91	$95.90	$95.90
7 purchase totals =	$716.08		$774.5163	$774.53	$774.50	$774.50