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	$16.76	10.631%	$18.5418	$18.54	$18.55	$18.50
Purchase #2	$192.37	9.371%	$210.397	$210.40	$210.40	$210.40
Purchase #3	$54.58	13.777%	$62.0995	$62.10	$62.10	$62.10
Purchase #4	$124.93	4.770%	$130.8892	$130.89	$130.90	$130.90
Purchase #5	$126.88	3.319%	$131.0911	$131.09	$131.10	$131.10
Purchase #6	$177.27	13.592%	$201.3645	$201.36	$201.35	$201.40
Purchase #7	$74.67	5.692%	$78.9202	$78.92	$78.90	$78.90
7 purchase totals =	$767.46		$833.3033	$833.30	$833.30	$833.30