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	$94.55	6.138%	$100.3535	$100.35	$100.35	$100.40
Purchase #2	$37.87	6.853%	$40.4652	$40.47	$40.45	$40.50
Purchase #3	$185.63	10.839%	$205.7504	$205.75	$205.75	$205.80
Purchase #4	$162.51	6.426%	$172.9529	$172.95	$172.95	$173.00
Purchase #5	$14.36	13.510%	$16.3	$16.30	$16.30	$16.30
Purchase #6	$90.91	4.604%	$95.0955	$95.10	$95.10	$95.10
Purchase #7	$222.89	6.526%	$237.4358	$237.44	$237.45	$237.40
7 purchase totals =	$808.72		$868.3533	$868.36	$868.35	$868.50