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	$21.33	5.777%	$22.5622	$22.56	$22.55	$22.60
Purchase #2	$98.83	3.262%	$102.0538	$102.05	$102.05	$102.10
Purchase #3	$207.37	6.752%	$221.3716	$221.37	$221.35	$221.40
Purchase #4	$38.28	4.765%	$40.104	$40.10	$40.10	$40.10
Purchase #5	$124.71	6.648%	$133.0007	$133.00	$133.00	$133.00
Purchase #6	$98.98	12.728%	$111.5782	$111.58	$111.60	$111.60
Purchase #7	$78.44	10.372%	$86.5758	$86.58	$86.60	$86.60
7 purchase totals =	$667.94		$717.2463	$717.24	$717.25	$717.40