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	$244.77	12.533%	$275.447	$275.45	$275.45	$275.40
Purchase #2	$175.47	10.822%	$194.4594	$194.46	$194.45	$194.50
Purchase #3	$50.85	8.279%	$55.0599	$55.06	$55.05	$55.10
Purchase #4	$56.69	4.246%	$59.0971	$59.10	$59.10	$59.10
Purchase #5	$86.38	6.836%	$92.2849	$92.28	$92.30	$92.30
Purchase #6	$218.60	13.272%	$247.6126	$247.61	$247.60	$247.60
Purchase #7	$243.62	6.662%	$259.85	$259.85	$259.85	$259.90
7 purchase totals =	$1,076.38		$1,183.8109	$1,183.81	$1,183.80	$1,183.90