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	$234.41	6.523%	$249.7006	$249.70	$249.70	$249.70
Purchase #2	$19.86	5.753%	$21.0025	$21.00	$21.00	$21.00
Purchase #3	$19.30	6.161%	$20.4891	$20.49	$20.50	$20.50
Purchase #4	$58.76	7.765%	$63.3227	$63.32	$63.30	$63.30
Purchase #5	$145.80	13.564%	$165.5763	$165.58	$165.60	$165.60
Purchase #6	$85.90	7.301%	$92.1716	$92.17	$92.15	$92.20
Purchase #7	$51.73	3.189%	$53.3797	$53.38	$53.40	$53.40
7 purchase totals =	$615.76		$665.6425	$665.64	$665.65	$665.70