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	$139.50	7.831%	$150.4242	$150.42	$150.40	$150.40
Purchase #2	$29.55	4.192%	$30.7887	$30.79	$30.80	$30.80
Purchase #3	$151.90	10.214%	$167.4151	$167.42	$167.40	$167.40
Purchase #4	$22.99	11.606%	$25.6582	$25.66	$25.65	$25.70
Purchase #5	$176.77	13.626%	$200.8567	$200.86	$200.85	$200.90
Purchase #6	$103.82	5.564%	$109.5965	$109.60	$109.60	$109.60
Purchase #7	$81.85	7.575%	$88.0501	$88.05	$88.05	$88.10
7 purchase totals =	$706.38		$772.7895	$772.80	$772.75	$772.90