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	$39.39	12.375%	$44.2645	$44.26	$44.25	$44.30
Purchase #2	$113.32	10.760%	$125.5132	$125.51	$125.50	$125.50
Purchase #3	$96.68	3.202%	$99.7757	$99.78	$99.80	$99.80
Purchase #4	$47.78	11.823%	$53.429	$53.43	$53.45	$53.40
Purchase #5	$74.99	8.357%	$81.2569	$81.26	$81.25	$81.30
Purchase #6	$80.89	12.195%	$90.7545	$90.75	$90.75	$90.80
Purchase #7	$77.70	9.804%	$85.3177	$85.32	$85.30	$85.30
7 purchase totals =	$530.75		$580.3115	$580.31	$580.30	$580.40