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	$35.32	13.306%	$40.0197	$40.02	$40.00	$40.00
Purchase #2	$67.70	5.608%	$71.4966	$71.50	$71.50	$71.50
Purchase #3	$169.47	7.658%	$182.448	$182.45	$182.45	$182.40
Purchase #4	$239.42	7.604%	$257.6255	$257.63	$257.65	$257.60
Purchase #5	$34.69	12.749%	$39.1126	$39.11	$39.10	$39.10
Purchase #6	$87.72	3.162%	$90.4937	$90.49	$90.50	$90.50
Purchase #7	$82.52	13.173%	$93.3904	$93.39	$93.40	$93.40
7 purchase totals =	$716.84		$774.5865	$774.59	$774.60	$774.50