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	$101.52	12.768%	$114.4821	$114.48	$114.50	$114.50
Purchase #2	$43.48	13.812%	$49.4855	$49.49	$49.50	$49.50
Purchase #3	$82.92	3.490%	$85.8139	$85.81	$85.80	$85.80
Purchase #4	$234.64	8.343%	$254.216	$254.22	$254.20	$254.20
Purchase #5	$87.66	3.436%	$90.672	$90.67	$90.65	$90.70
Purchase #6	$60.72	9.152%	$66.2771	$66.28	$66.30	$66.30
Purchase #7	$121.61	7.383%	$130.5885	$130.59	$130.60	$130.60
7 purchase totals =	$732.55		$791.5351	$791.54	$791.55	$791.60