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	$241.42	7.778%	$260.1976	$260.20	$260.20	$260.20
Purchase #2	$17.67	8.237%	$19.1255	$19.13	$19.15	$19.10
Purchase #3	$18.96	7.737%	$20.4269	$20.43	$20.45	$20.40
Purchase #4	$39.64	6.580%	$42.2483	$42.25	$42.25	$42.20
Purchase #5	$56.92	5.124%	$59.8366	$59.84	$59.85	$59.80
Purchase #6	$40.51	6.723%	$43.2335	$43.23	$43.25	$43.20
Purchase #7	$200.72	10.243%	$221.2797	$221.28	$221.30	$221.30
7 purchase totals =	$615.84		$666.3481	$666.36	$666.45	$666.20