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	$7.51	9.640%	$8.234	$8.23	$8.25	$8.20
Purchase #2	$210.84	9.154%	$230.1403	$230.14	$230.15	$230.10
Purchase #3	$155.88	5.589%	$164.5921	$164.59	$164.60	$164.60
Purchase #4	$96.42	6.215%	$102.4125	$102.41	$102.40	$102.40
Purchase #5	$217.50	10.300%	$239.9025	$239.90	$239.90	$239.90
Purchase #6	$157.72	5.139%	$165.8252	$165.83	$165.85	$165.80
Purchase #7	$230.29	13.677%	$261.7868	$261.79	$261.80	$261.80
7 purchase totals =	$1,076.16		$1,172.8934	$1,172.89	$1,172.95	$1,172.80