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	$20.97	3.137%	$21.6278	$21.63	$21.65	$21.60
Purchase #2	$102.55	9.615%	$112.4102	$112.41	$112.40	$112.40
Purchase #3	$184.78	11.111%	$205.3109	$205.31	$205.30	$205.30
Purchase #4	$49.74	8.532%	$53.9838	$53.98	$54.00	$54.00
Purchase #5	$40.98	3.473%	$42.4032	$42.40	$42.40	$42.40
Purchase #6	$42.97	3.667%	$44.5457	$44.55	$44.55	$44.50
Purchase #7	$213.52	4.591%	$223.3227	$223.32	$223.30	$223.30
7 purchase totals =	$655.51		$703.6043	$703.60	$703.60	$703.50