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	$77.85	8.387%	$84.3793	$84.38	$84.40	$84.40
Purchase #2	$75.25	13.575%	$85.4652	$85.47	$85.45	$85.50
Purchase #3	$92.28	11.616%	$102.9992	$103.00	$103.00	$103.00
Purchase #4	$166.59	11.426%	$185.6246	$185.62	$185.60	$185.60
Purchase #5	$46.43	13.199%	$52.5583	$52.56	$52.55	$52.60
Purchase #6	$200.79	7.391%	$215.6304	$215.63	$215.65	$215.60
Purchase #7	$80.42	10.757%	$89.0708	$89.07	$89.05	$89.10
7 purchase totals =	$739.61		$815.7278	$815.73	$815.70	$815.80