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	$19.74	4.620%	$20.652	$20.65	$20.65	$20.70
Purchase #2	$243.29	5.860%	$257.5468	$257.55	$257.55	$257.50
Purchase #3	$156.40	12.507%	$175.9609	$175.96	$175.95	$176.00
Purchase #4	$127.48	13.312%	$144.4501	$144.45	$144.45	$144.50
Purchase #5	$36.60	7.305%	$39.2736	$39.27	$39.25	$39.30
Purchase #6	$56.59	4.729%	$59.2661	$59.27	$59.25	$59.30
Purchase #7	$228.43	9.186%	$249.4136	$249.41	$249.40	$249.40
7 purchase totals =	$868.53		$946.5631	$946.56	$946.50	$946.70