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	$173.87	6.672%	$185.4706	$185.47	$185.45	$185.50
Purchase #2	$105.82	11.531%	$118.0221	$118.02	$118.00	$118.00
Purchase #3	$163.96	4.595%	$171.494	$171.49	$171.50	$171.50
Purchase #4	$125.99	12.254%	$141.4288	$141.43	$141.45	$141.40
Purchase #5	$79.93	3.588%	$82.7979	$82.80	$82.80	$82.80
Purchase #6	$153.96	10.840%	$170.6493	$170.65	$170.65	$170.60
Purchase #7	$160.51	5.542%	$169.4055	$169.41	$169.40	$169.40
7 purchase totals =	$964.04		$1,039.2682	$1,039.27	$1,039.25	$1,039.20