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	$28.90	3.798%	$29.9976	$30.00	$30.00	$30.00
Purchase #2	$98.80	6.596%	$105.3168	$105.32	$105.30	$105.30
Purchase #3	$42.53	4.623%	$44.4962	$44.50	$44.50	$44.50
Purchase #4	$55.43	7.262%	$59.4553	$59.46	$59.45	$59.50
Purchase #5	$231.43	10.445%	$255.6029	$255.60	$255.60	$255.60
Purchase #6	$224.76	12.148%	$252.0638	$252.06	$252.05	$252.10
Purchase #7	$23.34	13.169%	$26.4136	$26.41	$26.40	$26.40
7 purchase totals =	$705.19		$773.3462	$773.35	$773.30	$773.40