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	$15.55	5.546%	$16.4124	$16.41	$16.40	$16.40
Purchase #2	$168.59	6.788%	$180.0339	$180.03	$180.05	$180.00
Purchase #3	$131.58	11.287%	$146.4314	$146.43	$146.45	$146.40
Purchase #4	$145.62	4.667%	$152.4161	$152.42	$152.40	$152.40
Purchase #5	$89.87	9.364%	$98.2854	$98.29	$98.30	$98.30
Purchase #6	$50.38	7.426%	$54.1212	$54.12	$54.10	$54.10
Purchase #7	$89.65	7.449%	$96.328	$96.33	$96.35	$96.30
7 purchase totals =	$691.24		$744.0284	$744.03	$744.05	$743.90