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	$95.42	12.332%	$107.1872	$107.19	$107.20	$107.20
Purchase #2	$196.54	11.301%	$218.751	$218.75	$218.75	$218.80
Purchase #3	$82.97	8.396%	$89.9362	$89.94	$89.95	$89.90
Purchase #4	$88.65	13.567%	$100.6771	$100.68	$100.70	$100.70
Purchase #5	$227.64	6.433%	$242.2841	$242.28	$242.30	$242.30
Purchase #6	$42.92	13.623%	$48.767	$48.77	$48.75	$48.80
Purchase #7	$169.52	13.813%	$192.9358	$192.94	$192.95	$192.90
7 purchase totals =	$903.66		$1,000.5384	$1,000.55	$1,000.60	$1,000.60