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	$250.88	11.625%	$280.0448	$280.04	$280.05	$280.00
Purchase #2	$29.41	6.496%	$31.3205	$31.32	$31.30	$31.30
Purchase #3	$55.99	12.118%	$62.7749	$62.77	$62.75	$62.80
Purchase #4	$34.65	8.297%	$37.5249	$37.52	$37.50	$37.50
Purchase #5	$247.94	5.785%	$262.2833	$262.28	$262.30	$262.30
Purchase #6	$218.99	11.489%	$244.1498	$244.15	$244.15	$244.10
Purchase #7	$177.61	10.591%	$196.4207	$196.42	$196.40	$196.40
7 purchase totals =	$1,015.47		$1,114.5189	$1,114.50	$1,114.45	$1,114.40