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	$161.48	4.122%	$168.1362	$168.14	$168.15	$168.10
Purchase #2	$35.30	11.126%	$39.2275	$39.23	$39.25	$39.20
Purchase #3	$142.34	9.378%	$155.6886	$155.69	$155.70	$155.70
Purchase #4	$29.50	6.200%	$31.329	$31.33	$31.35	$31.30
Purchase #5	$89.95	13.103%	$101.7361	$101.74	$101.75	$101.70
Purchase #6	$40.72	5.784%	$43.0752	$43.08	$43.10	$43.10
Purchase #7	$47.98	10.204%	$52.8759	$52.88	$52.90	$52.90
7 purchase totals =	$547.27		$592.0685	$592.09	$592.20	$592.00