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	$245.84	4.128%	$255.9883	$255.99	$256.00	$256.00
Purchase #2	$169.78	7.379%	$182.3081	$182.31	$182.30	$182.30
Purchase #3	$165.62	3.540%	$171.4829	$171.48	$171.50	$171.50
Purchase #4	$144.83	5.359%	$152.5914	$152.59	$152.60	$152.60
Purchase #5	$31.86	5.475%	$33.6043	$33.60	$33.60	$33.60
Purchase #6	$213.81	11.207%	$237.7717	$237.77	$237.75	$237.80
Purchase #7	$51.99	6.597%	$55.4198	$55.42	$55.40	$55.40
7 purchase totals =	$1,023.73		$1,089.1665	$1,089.16	$1,089.15	$1,089.20