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	$60.25	4.554%	$62.9938	$62.99	$63.00	$63.00
Purchase #2	$75.61	3.765%	$78.4567	$78.46	$78.45	$78.50
Purchase #3	$89.75	7.446%	$96.4328	$96.43	$96.45	$96.40
Purchase #4	$49.37	4.852%	$51.7654	$51.77	$51.75	$51.80
Purchase #5	$23.87	4.162%	$24.8635	$24.86	$24.85	$24.90
Purchase #6	$152.89	4.210%	$159.3267	$159.33	$159.35	$159.30
Purchase #7	$159.67	5.161%	$167.9106	$167.91	$167.90	$167.90
7 purchase totals =	$611.41		$641.7495	$641.75	$641.75	$641.80