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	$105.49	5.814%	$111.6232	$111.62	$111.60	$111.60
Purchase #2	$62.84	4.813%	$65.8645	$65.86	$65.85	$65.90
Purchase #3	$177.29	8.238%	$191.8952	$191.90	$191.90	$191.90
Purchase #4	$84.82	6.493%	$90.3274	$90.33	$90.35	$90.30
Purchase #5	$158.99	11.567%	$177.3804	$177.38	$177.40	$177.40
Purchase #6	$159.47	4.818%	$167.1533	$167.15	$167.15	$167.20
Purchase #7	$33.96	12.252%	$38.1208	$38.12	$38.10	$38.10
7 purchase totals =	$782.86		$842.3648	$842.36	$842.35	$842.40