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	$248.39	9.759%	$272.6304	$272.63	$272.65	$272.60
Purchase #2	$116.37	9.371%	$127.275	$127.28	$127.30	$127.30
Purchase #3	$100.63	10.700%	$111.3974	$111.40	$111.40	$111.40
Purchase #4	$187.79	12.808%	$211.8421	$211.84	$211.85	$211.80
Purchase #5	$194.56	4.779%	$203.858	$203.86	$203.85	$203.90
Purchase #6	$34.41	12.519%	$38.7178	$38.72	$38.70	$38.70
Purchase #7	$60.98	4.811%	$63.9137	$63.91	$63.90	$63.90
7 purchase totals =	$943.13		$1,029.6344	$1,029.64	$1,029.65	$1,029.60