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	$59.93	10.195%	$66.0399	$66.04	$66.05	$66.00
Purchase #2	$168.94	13.624%	$191.9564	$191.96	$191.95	$192.00
Purchase #3	$17.95	4.769%	$18.806	$18.81	$18.80	$18.80
Purchase #4	$164.93	10.648%	$182.4917	$182.49	$182.50	$182.50
Purchase #5	$83.42	7.848%	$89.9668	$89.97	$89.95	$90.00
Purchase #6	$185.50	7.859%	$200.0784	$200.08	$200.10	$200.10
Purchase #7	$112.71	7.322%	$120.9626	$120.96	$120.95	$121.00
7 purchase totals =	$793.38		$870.3018	$870.31	$870.30	$870.40