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	$181.65	13.702%	$206.5397	$206.54	$206.55	$206.50
Purchase #2	$66.29	9.437%	$72.5458	$72.55	$72.55	$72.50
Purchase #3	$116.64	8.806%	$126.9113	$126.91	$126.90	$126.90
Purchase #4	$74.70	7.656%	$80.419	$80.42	$80.40	$80.40
Purchase #5	$72.92	13.149%	$82.5083	$82.51	$82.50	$82.50
Purchase #6	$33.73	8.420%	$36.5701	$36.57	$36.55	$36.60
Purchase #7	$138.92	8.171%	$150.2712	$150.27	$150.25	$150.30
7 purchase totals =	$684.85		$755.7654	$755.77	$755.70	$755.70