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	$8.90	4.686%	$9.3171	$9.32	$9.30	$9.30
Purchase #2	$201.98	8.674%	$219.4997	$219.50	$219.50	$219.50
Purchase #3	$103.94	12.314%	$116.7392	$116.74	$116.75	$116.70
Purchase #4	$145.30	11.571%	$162.1127	$162.11	$162.10	$162.10
Purchase #5	$94.87	6.262%	$100.8108	$100.81	$100.80	$100.80
Purchase #6	$56.59	5.184%	$59.5236	$59.52	$59.50	$59.50
Purchase #7	$13.50	7.651%	$14.5329	$14.53	$14.55	$14.50
7 purchase totals =	$625.08		$682.5360	$682.53	$682.50	$682.40