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	$57.29	12.159%	$64.2559	$64.26	$64.25	$64.30
Purchase #2	$152.97	11.828%	$171.0633	$171.06	$171.05	$171.10
Purchase #3	$87.35	5.646%	$92.2818	$92.28	$92.30	$92.30
Purchase #4	$69.43	3.616%	$71.9406	$71.94	$71.95	$71.90
Purchase #5	$138.53	9.527%	$151.7278	$151.73	$151.75	$151.70
Purchase #6	$213.34	8.492%	$231.4568	$231.46	$231.45	$231.50
Purchase #7	$13.31	11.392%	$14.8263	$14.83	$14.85	$14.80
7 purchase totals =	$732.22		$797.5525	$797.56	$797.60	$797.60