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	$16.99	11.591%	$18.9593	$18.96	$18.95	$19.00
Purchase #2	$18.34	9.103%	$20.0095	$20.01	$20.00	$20.00
Purchase #3	$39.50	13.578%	$44.8633	$44.86	$44.85	$44.90
Purchase #4	$164.52	6.630%	$175.4277	$175.43	$175.45	$175.40
Purchase #5	$121.36	8.623%	$131.8249	$131.82	$131.80	$131.80
Purchase #6	$33.87	13.519%	$38.4489	$38.45	$38.45	$38.40
Purchase #7	$218.71	7.223%	$234.5074	$234.51	$234.50	$234.50
7 purchase totals =	$613.29		$664.0410	$664.04	$664.00	$664.00