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	$16.41	6.625%	$17.4972	$17.50	$17.50	$17.50
Purchase #2	$215.90	12.296%	$242.4471	$242.45	$242.45	$242.40
Purchase #3	$38.37	13.408%	$43.5146	$43.51	$43.50	$43.50
Purchase #4	$196.71	13.322%	$222.9157	$222.92	$222.90	$222.90
Purchase #5	$32.44	6.794%	$34.644	$34.64	$34.65	$34.60
Purchase #6	$158.42	10.121%	$174.4537	$174.45	$174.45	$174.50
Purchase #7	$95.88	3.710%	$99.4371	$99.44	$99.45	$99.40
7 purchase totals =	$754.13		$834.9094	$834.91	$834.90	$834.80