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	$44.64	7.843%	$48.1411	$48.14	$48.15	$48.10
Purchase #2	$77.36	6.574%	$82.4456	$82.45	$82.45	$82.40
Purchase #3	$230.89	6.366%	$245.5885	$245.59	$245.60	$245.60
Purchase #4	$126.37	6.674%	$134.8039	$134.80	$134.80	$134.80
Purchase #5	$210.74	5.561%	$222.4593	$222.46	$222.45	$222.50
Purchase #6	$137.51	4.800%	$144.1105	$144.11	$144.10	$144.10
Purchase #7	$102.93	9.181%	$112.38	$112.38	$112.40	$112.40
7 purchase totals =	$930.44		$989.9289	$989.93	$989.95	$989.90