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	$31.42	9.367%	$34.3631	$34.36	$34.35	$34.40
Purchase #2	$59.76	7.748%	$64.3902	$64.39	$64.40	$64.40
Purchase #3	$112.25	3.743%	$116.4515	$116.45	$116.45	$116.50
Purchase #4	$165.63	12.437%	$186.2294	$186.23	$186.25	$186.20
Purchase #5	$218.56	7.142%	$234.1696	$234.17	$234.15	$234.20
Purchase #6	$96.58	3.671%	$100.1255	$100.13	$100.15	$100.10
Purchase #7	$146.50	12.513%	$164.8315	$164.83	$164.85	$164.80
7 purchase totals =	$830.70		$900.5608	$900.56	$900.60	$900.60