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	$39.80	6.229%	$42.2791	$42.28	$42.30	$42.30
Purchase #2	$128.79	13.192%	$145.78	$145.78	$145.80	$145.80
Purchase #3	$139.42	13.793%	$158.6502	$158.65	$158.65	$158.70
Purchase #4	$37.86	9.329%	$41.392	$41.39	$41.40	$41.40
Purchase #5	$249.43	6.631%	$265.9697	$265.97	$265.95	$266.00
Purchase #6	$65.75	5.322%	$69.2492	$69.25	$69.25	$69.20
Purchase #7	$95.26	8.274%	$103.1418	$103.14	$103.15	$103.10
7 purchase totals =	$756.31		$826.4620	$826.46	$826.50	$826.50