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	$40.56	10.450%	$44.7985	$44.80	$44.80	$44.80
Purchase #2	$112.25	6.358%	$119.3869	$119.39	$119.40	$119.40
Purchase #3	$75.34	4.541%	$78.7612	$78.76	$78.75	$78.80
Purchase #4	$206.86	6.242%	$219.7722	$219.77	$219.75	$219.80
Purchase #5	$52.64	8.199%	$56.956	$56.96	$56.95	$57.00
Purchase #6	$72.87	7.119%	$78.0576	$78.06	$78.05	$78.10
Purchase #7	$102.67	9.256%	$112.1731	$112.17	$112.15	$112.20
7 purchase totals =	$663.19		$709.9055	$709.91	$709.85	$710.10