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	$222.79	12.212%	$249.9971	$250.00	$250.00	$250.00
Purchase #2	$217.56	9.705%	$238.6742	$238.67	$238.65	$238.70
Purchase #3	$71.66	3.656%	$74.2799	$74.28	$74.30	$74.30
Purchase #4	$78.99	8.258%	$85.513	$85.51	$85.50	$85.50
Purchase #5	$41.41	6.855%	$44.2487	$44.25	$44.25	$44.20
Purchase #6	$75.31	4.422%	$78.6402	$78.64	$78.65	$78.60
Purchase #7	$96.82	3.800%	$100.4992	$100.50	$100.50	$100.50
7 purchase totals =	$804.54		$871.8523	$871.85	$871.85	$871.80