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	$112.55	12.231%	$126.316	$126.32	$126.30	$126.30
Purchase #2	$48.65	12.859%	$54.9059	$54.91	$54.90	$54.90
Purchase #3	$192.91	3.874%	$200.3833	$200.38	$200.40	$200.40
Purchase #4	$211.64	10.162%	$233.1469	$233.15	$233.15	$233.10
Purchase #5	$37.30	8.737%	$40.5589	$40.56	$40.55	$40.60
Purchase #6	$44.55	10.118%	$49.0576	$49.06	$49.05	$49.10
Purchase #7	$133.51	3.791%	$138.5714	$138.57	$138.55	$138.60
7 purchase totals =	$781.11		$842.9400	$842.95	$842.90	$843.00