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	$43.61	11.123%	$48.4607	$48.46	$48.45	$48.50
Purchase #2	$244.87	10.496%	$270.5716	$270.57	$270.55	$270.60
Purchase #3	$82.92	9.601%	$90.8811	$90.88	$90.90	$90.90
Purchase #4	$178.99	6.307%	$190.2789	$190.28	$190.30	$190.30
Purchase #5	$114.52	7.674%	$123.3083	$123.31	$123.30	$123.30
Purchase #6	$108.42	10.545%	$119.8529	$119.85	$119.85	$119.90
Purchase #7	$210.83	11.366%	$234.7929	$234.79	$234.80	$234.80
7 purchase totals =	$984.16		$1,078.1464	$1,078.14	$1,078.15	$1,078.30