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	$151.57	8.408%	$164.314	$164.31	$164.30	$164.30
Purchase #2	$141.50	4.786%	$148.2722	$148.27	$148.25	$148.30
Purchase #3	$18.81	12.755%	$21.2092	$21.21	$21.20	$21.20
Purchase #4	$166.78	10.288%	$183.9383	$183.94	$183.95	$183.90
Purchase #5	$10.64	7.432%	$11.4308	$11.43	$11.45	$11.40
Purchase #6	$128.58	12.824%	$145.0691	$145.07	$145.05	$145.10
Purchase #7	$84.28	9.331%	$92.1442	$92.14	$92.15	$92.10
7 purchase totals =	$702.16		$766.3778	$766.37	$766.35	$766.30