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	$150.45	10.736%	$166.6023	$166.60	$166.60	$166.60
Purchase #2	$232.88	13.759%	$264.922	$264.92	$264.90	$264.90
Purchase #3	$214.50	8.658%	$233.0714	$233.07	$233.05	$233.10
Purchase #4	$70.44	3.391%	$72.8286	$72.83	$72.85	$72.80
Purchase #5	$140.91	10.590%	$155.8324	$155.83	$155.85	$155.80
Purchase #6	$111.52	6.817%	$119.1223	$119.12	$119.10	$119.10
Purchase #7	$151.76	6.739%	$161.9871	$161.99	$162.00	$162.00
7 purchase totals =	$1,072.46		$1,174.3661	$1,174.36	$1,174.35	$1,174.30