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	$113.42	9.406%	$124.0883	$124.09	$124.10	$124.10
Purchase #2	$7.69	9.141%	$8.3929	$8.39	$8.40	$8.40
Purchase #3	$183.53	7.152%	$196.6561	$196.66	$196.65	$196.70
Purchase #4	$120.84	9.500%	$132.3198	$132.32	$132.30	$132.30
Purchase #5	$82.70	5.149%	$86.9582	$86.96	$86.95	$87.00
Purchase #6	$133.33	6.554%	$142.0684	$142.07	$142.05	$142.10
Purchase #7	$178.54	12.497%	$200.8521	$200.85	$200.85	$200.90
7 purchase totals =	$820.05		$891.3358	$891.34	$891.30	$891.50