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	$123.33	3.393%	$127.5146	$127.51	$127.50	$127.50
Purchase #2	$19.58	7.172%	$20.9843	$20.98	$21.00	$21.00
Purchase #3	$226.48	7.523%	$243.5181	$243.52	$243.50	$243.50
Purchase #4	$220.29	13.698%	$250.4653	$250.47	$250.45	$250.50
Purchase #5	$20.47	5.511%	$21.5981	$21.60	$21.60	$21.60
Purchase #6	$74.56	12.541%	$83.9106	$83.91	$83.90	$83.90
Purchase #7	$224.97	7.315%	$241.4266	$241.43	$241.45	$241.40
7 purchase totals =	$909.68		$989.4176	$989.42	$989.40	$989.40