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	$135.33	6.577%	$144.2307	$144.23	$144.25	$144.20
Purchase #2	$32.67	12.532%	$36.7642	$36.76	$36.75	$36.80
Purchase #3	$50.64	12.449%	$56.9442	$56.94	$56.95	$56.90
Purchase #4	$244.30	6.429%	$260.006	$260.01	$260.00	$260.00
Purchase #5	$40.31	5.363%	$42.4718	$42.47	$42.45	$42.50
Purchase #6	$47.61	4.310%	$49.662	$49.66	$49.65	$49.70
Purchase #7	$94.39	9.500%	$103.3571	$103.36	$103.35	$103.40
7 purchase totals =	$645.25		$693.4360	$693.43	$693.40	$693.50