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	$104.67	4.639%	$109.5256	$109.53	$109.55	$109.50
Purchase #2	$35.71	6.202%	$37.9247	$37.92	$37.90	$37.90
Purchase #3	$47.47	7.783%	$51.1646	$51.16	$51.15	$51.20
Purchase #4	$236.78	8.154%	$256.087	$256.09	$256.10	$256.10
Purchase #5	$214.53	13.147%	$242.7343	$242.73	$242.75	$242.70
Purchase #6	$41.70	5.308%	$43.9134	$43.91	$43.90	$43.90
Purchase #7	$212.48	10.420%	$234.6204	$234.62	$234.60	$234.60
7 purchase totals =	$893.34		$975.9700	$975.96	$975.95	$975.90