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	$44.72	6.210%	$47.4971	$47.50	$47.50	$47.50
Purchase #2	$123.66	10.255%	$136.3413	$136.34	$136.35	$136.30
Purchase #3	$96.38	3.778%	$100.0212	$100.02	$100.00	$100.00
Purchase #4	$192.27	9.288%	$210.128	$210.13	$210.15	$210.10
Purchase #5	$131.69	9.333%	$143.9806	$143.98	$144.00	$144.00
Purchase #6	$249.39	10.645%	$275.9376	$275.94	$275.95	$275.90
Purchase #7	$167.25	5.592%	$176.6026	$176.60	$176.60	$176.60
7 purchase totals =	$1,005.36		$1,090.5084	$1,090.51	$1,090.55	$1,090.40