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	$178.56	3.609%	$185.0042	$185.00	$185.00	$185.00
Purchase #2	$110.95	11.321%	$123.5106	$123.51	$123.50	$123.50
Purchase #3	$39.38	8.538%	$42.7423	$42.74	$42.75	$42.70
Purchase #4	$151.90	3.599%	$157.3669	$157.37	$157.35	$157.40
Purchase #5	$167.57	3.214%	$172.9557	$172.96	$172.95	$173.00
Purchase #6	$250.45	3.177%	$258.4068	$258.41	$258.40	$258.40
Purchase #7	$33.90	13.720%	$38.5511	$38.55	$38.55	$38.60
7 purchase totals =	$932.71		$978.5376	$978.54	$978.50	$978.60