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	$37.51	10.641%	$41.5014	$41.50	$41.50	$41.50
Purchase #2	$102.76	7.147%	$110.1043	$110.10	$110.10	$110.10
Purchase #3	$73.77	13.704%	$83.8794	$83.88	$83.90	$83.90
Purchase #4	$100.50	11.498%	$112.0555	$112.06	$112.05	$112.10
Purchase #5	$17.85	4.301%	$18.6177	$18.62	$18.60	$18.60
Purchase #6	$77.98	9.299%	$85.2314	$85.23	$85.25	$85.20
Purchase #7	$233.27	8.488%	$253.07	$253.07	$253.05	$253.10
7 purchase totals =	$643.64		$704.4597	$704.46	$704.45	$704.50