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	$57.47	12.857%	$64.8589	$64.86	$64.85	$64.90
Purchase #2	$87.74	7.826%	$94.6065	$94.61	$94.60	$94.60
Purchase #3	$117.96	13.314%	$133.6652	$133.67	$133.65	$133.70
Purchase #4	$65.73	10.240%	$72.4608	$72.46	$72.45	$72.50
Purchase #5	$46.71	3.649%	$48.4144	$48.41	$48.40	$48.40
Purchase #6	$74.88	9.810%	$82.2257	$82.23	$82.25	$82.20
Purchase #7	$53.46	13.720%	$60.7947	$60.79	$60.80	$60.80
7 purchase totals =	$503.95		$557.0262	$557.03	$557.00	$557.10