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	$72.90	9.206%	$79.6112	$79.61	$79.60	$79.60
Purchase #2	$127.42	13.590%	$144.7364	$144.74	$144.75	$144.70
Purchase #3	$35.96	4.358%	$37.5271	$37.53	$37.55	$37.50
Purchase #4	$80.68	12.358%	$90.6504	$90.65	$90.65	$90.70
Purchase #5	$95.85	7.359%	$102.9036	$102.90	$102.90	$102.90
Purchase #6	$47.74	5.161%	$50.2039	$50.20	$50.20	$50.20
Purchase #7	$136.89	4.696%	$143.3184	$143.32	$143.30	$143.30
7 purchase totals =	$597.44		$648.9510	$648.95	$648.95	$648.90