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	$223.80	12.292%	$251.3095	$251.31	$251.30	$251.30
Purchase #2	$75.62	9.381%	$82.7139	$82.71	$82.70	$82.70
Purchase #3	$48.65	12.154%	$54.5629	$54.56	$54.55	$54.60
Purchase #4	$197.76	7.768%	$213.122	$213.12	$213.10	$213.10
Purchase #5	$109.70	12.594%	$123.5156	$123.52	$123.50	$123.50
Purchase #6	$173.73	4.715%	$181.9214	$181.92	$181.90	$181.90
Purchase #7	$155.66	7.565%	$167.4357	$167.44	$167.45	$167.40
7 purchase totals =	$984.92		$1,074.5810	$1,074.58	$1,074.50	$1,074.50