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	$39.85	6.584%	$42.4737	$42.47	$42.45	$42.50
Purchase #2	$57.89	6.818%	$61.8369	$61.84	$61.85	$61.80
Purchase #3	$106.69	12.508%	$120.0348	$120.03	$120.05	$120.00
Purchase #4	$117.99	10.380%	$130.2374	$130.24	$130.25	$130.20
Purchase #5	$163.77	6.651%	$174.6623	$174.66	$174.65	$174.70
Purchase #6	$41.69	4.445%	$43.5431	$43.54	$43.55	$43.50
Purchase #7	$227.25	12.267%	$255.1268	$255.13	$255.15	$255.10
7 purchase totals =	$755.13		$827.9150	$827.91	$827.95	$827.80