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	$23.54	3.406%	$24.3418	$24.34	$24.35	$24.30
Purchase #2	$207.43	3.413%	$214.5096	$214.51	$214.50	$214.50
Purchase #3	$35.75	11.418%	$39.8319	$39.83	$39.85	$39.80
Purchase #4	$105.87	5.692%	$111.8961	$111.90	$111.90	$111.90
Purchase #5	$30.59	3.110%	$31.5413	$31.54	$31.55	$31.50
Purchase #6	$195.68	13.619%	$222.3297	$222.33	$222.35	$222.30
Purchase #7	$166.55	10.352%	$183.7913	$183.79	$183.80	$183.80
7 purchase totals =	$765.41		$828.2417	$828.24	$828.30	$828.10