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	$51.75	12.426%	$58.1805	$58.18	$58.20	$58.20
Purchase #2	$82.58	13.189%	$93.4715	$93.47	$93.45	$93.50
Purchase #3	$203.91	9.774%	$223.8402	$223.84	$223.85	$223.80
Purchase #4	$99.46	3.586%	$103.0266	$103.03	$103.05	$103.00
Purchase #5	$98.54	12.230%	$110.5914	$110.59	$110.60	$110.60
Purchase #6	$226.61	3.638%	$234.8541	$234.85	$234.85	$234.90
Purchase #7	$111.77	10.846%	$123.8926	$123.89	$123.90	$123.90
7 purchase totals =	$874.62		$947.8569	$947.85	$947.90	$947.90