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	$58.42	9.370%	$63.894	$63.89	$63.90	$63.90
Purchase #2	$123.71	4.298%	$129.0271	$129.03	$129.05	$129.00
Purchase #3	$41.58	9.636%	$45.5866	$45.59	$45.60	$45.60
Purchase #4	$87.69	6.738%	$93.5986	$93.60	$93.60	$93.60
Purchase #5	$38.45	10.784%	$42.5964	$42.60	$42.60	$42.60
Purchase #6	$218.30	12.419%	$245.4107	$245.41	$245.40	$245.40
Purchase #7	$83.60	8.590%	$90.7812	$90.78	$90.80	$90.80
7 purchase totals =	$651.75		$710.8946	$710.90	$710.95	$710.90