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	$24.76	9.636%	$27.1459	$27.15	$27.15	$27.10
Purchase #2	$158.29	3.861%	$164.4016	$164.40	$164.40	$164.40
Purchase #3	$90.39	13.497%	$102.5899	$102.59	$102.60	$102.60
Purchase #4	$152.67	5.369%	$160.8669	$160.87	$160.85	$160.90
Purchase #5	$83.45	8.526%	$90.5649	$90.56	$90.55	$90.60
Purchase #6	$78.80	13.448%	$89.397	$89.40	$89.40	$89.40
Purchase #7	$58.77	6.801%	$62.7669	$62.77	$62.75	$62.80
7 purchase totals =	$647.13		$697.7331	$697.74	$697.70	$697.80