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	$69.83	12.555%	$78.5972	$78.60	$78.60	$78.60
Purchase #2	$58.61	6.700%	$62.5369	$62.54	$62.55	$62.50
Purchase #3	$46.44	5.336%	$48.918	$48.92	$48.90	$48.90
Purchase #4	$58.68	3.395%	$60.6722	$60.67	$60.65	$60.70
Purchase #5	$56.31	10.582%	$62.2687	$62.27	$62.25	$62.30
Purchase #6	$33.63	4.756%	$35.2294	$35.23	$35.25	$35.20
Purchase #7	$82.74	9.549%	$90.6408	$90.64	$90.65	$90.60
7 purchase totals =	$406.24		$438.8632	$438.87	$438.85	$438.80