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	$99.47	7.391%	$106.8218	$106.82	$106.80	$106.80
Purchase #2	$151.88	8.488%	$164.7716	$164.77	$164.75	$164.80
Purchase #3	$79.60	10.387%	$87.8681	$87.87	$87.85	$87.90
Purchase #4	$85.49	4.610%	$89.4311	$89.43	$89.45	$89.40
Purchase #5	$105.77	6.538%	$112.6852	$112.69	$112.70	$112.70
Purchase #6	$28.25	13.666%	$32.1106	$32.11	$32.10	$32.10
Purchase #7	$170.40	12.845%	$192.2879	$192.29	$192.30	$192.30
7 purchase totals =	$720.86		$785.9763	$785.98	$785.95	$786.00