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	$26.92	11.138%	$29.9183	$29.92	$29.90	$29.90
Purchase #2	$77.71	6.239%	$82.5583	$82.56	$82.55	$82.60
Purchase #3	$31.88	3.452%	$32.9805	$32.98	$33.00	$33.00
Purchase #4	$114.29	8.244%	$123.7121	$123.71	$123.70	$123.70
Purchase #5	$21.47	7.635%	$23.1092	$23.11	$23.10	$23.10
Purchase #6	$33.40	4.275%	$34.8279	$34.83	$34.85	$34.80
Purchase #7	$41.37	3.641%	$42.8763	$42.88	$42.90	$42.90
7 purchase totals =	$347.04		$369.9826	$369.99	$370.00	$370.00