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	$14.50	6.729%	$15.4757	$15.48	$15.50	$15.50
Purchase #2	$171.82	4.549%	$179.6361	$179.64	$179.65	$179.60
Purchase #3	$98.54	10.337%	$108.7261	$108.73	$108.75	$108.70
Purchase #4	$38.87	9.580%	$42.5937	$42.59	$42.60	$42.60
Purchase #5	$121.53	12.806%	$137.0931	$137.09	$137.10	$137.10
Purchase #6	$156.94	6.871%	$167.7233	$167.72	$167.70	$167.70
Purchase #7	$33.68	6.594%	$35.9009	$35.90	$35.90	$35.90
7 purchase totals =	$635.88		$687.1489	$687.15	$687.20	$687.10