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	$87.56	6.137%	$92.9336	$92.93	$92.95	$92.90
Purchase #2	$58.25	7.792%	$62.7888	$62.79	$62.80	$62.80
Purchase #3	$67.33	8.240%	$72.878	$72.88	$72.90	$72.90
Purchase #4	$123.45	5.201%	$129.8706	$129.87	$129.85	$129.90
Purchase #5	$188.82	4.110%	$196.5805	$196.58	$196.60	$196.60
Purchase #6	$37.43	3.294%	$38.6629	$38.66	$38.65	$38.70
Purchase #7	$224.63	9.629%	$246.2596	$246.26	$246.25	$246.30
7 purchase totals =	$787.47		$839.9740	$839.97	$840.00	$840.10