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	$101.66	11.671%	$113.5247	$113.52	$113.50	$113.50
Purchase #2	$82.61	8.246%	$89.422	$89.42	$89.40	$89.40
Purchase #3	$84.31	5.648%	$89.0718	$89.07	$89.05	$89.10
Purchase #4	$19.35	4.467%	$20.2144	$20.21	$20.20	$20.20
Purchase #5	$162.60	7.155%	$174.234	$174.23	$174.25	$174.20
Purchase #6	$5.47	13.533%	$6.2103	$6.21	$6.20	$6.20
Purchase #7	$176.86	8.371%	$191.665	$191.67	$191.65	$191.70
7 purchase totals =	$632.86		$684.3422	$684.33	$684.25	$684.30