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	$83.84	3.711%	$86.9513	$86.95	$86.95	$87.00
Purchase #2	$107.90	4.177%	$112.407	$112.41	$112.40	$112.40
Purchase #3	$163.64	13.769%	$186.1716	$186.17	$186.15	$186.20
Purchase #4	$65.68	8.832%	$71.4809	$71.48	$71.50	$71.50
Purchase #5	$41.34	5.640%	$43.6716	$43.67	$43.65	$43.70
Purchase #6	$132.56	9.287%	$144.8708	$144.87	$144.85	$144.90
Purchase #7	$172.76	13.607%	$196.2675	$196.27	$196.25	$196.30
7 purchase totals =	$767.72		$841.8207	$841.82	$841.75	$842.00