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	$37.79	6.502%	$40.2471	$40.25	$40.25	$40.20
Purchase #2	$56.76	8.853%	$61.785	$61.79	$61.80	$61.80
Purchase #3	$96.30	11.448%	$107.3244	$107.32	$107.30	$107.30
Purchase #4	$97.26	12.831%	$109.7394	$109.74	$109.75	$109.70
Purchase #5	$38.29	11.784%	$42.8021	$42.80	$42.80	$42.80
Purchase #6	$56.83	4.364%	$59.3101	$59.31	$59.30	$59.30
Purchase #7	$142.81	3.183%	$147.3556	$147.36	$147.35	$147.40
7 purchase totals =	$526.04		$568.5637	$568.57	$568.55	$568.50