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	$68.89	11.196%	$76.6029	$76.60	$76.60	$76.60
Purchase #2	$109.63	5.426%	$115.5785	$115.58	$115.60	$115.60
Purchase #3	$91.84	6.810%	$98.0943	$98.09	$98.10	$98.10
Purchase #4	$98.35	6.238%	$104.4851	$104.49	$104.50	$104.50
Purchase #5	$176.39	11.415%	$196.5249	$196.52	$196.50	$196.50
Purchase #6	$207.31	8.155%	$224.2161	$224.22	$224.20	$224.20
Purchase #7	$22.89	4.258%	$23.8647	$23.86	$23.85	$23.90
7 purchase totals =	$775.30		$839.3665	$839.36	$839.35	$839.40