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	$225.46	5.691%	$238.2909	$238.29	$238.30	$238.30
Purchase #2	$128.53	10.212%	$141.6555	$141.66	$141.65	$141.70
Purchase #3	$52.88	3.662%	$54.8165	$54.82	$54.80	$54.80
Purchase #4	$117.49	12.115%	$131.7239	$131.72	$131.70	$131.70
Purchase #5	$197.77	10.675%	$218.8819	$218.88	$218.90	$218.90
Purchase #6	$140.83	3.491%	$145.7464	$145.75	$145.75	$145.70
Purchase #7	$249.92	3.286%	$258.1324	$258.13	$258.15	$258.10
7 purchase totals =	$1,112.88		$1,189.2475	$1,189.25	$1,189.25	$1,189.20