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	$95.43	9.296%	$104.3012	$104.30	$104.30	$104.30
Purchase #2	$77.43	4.495%	$80.9105	$80.91	$80.90	$80.90
Purchase #3	$87.96	4.476%	$91.8971	$91.90	$91.90	$91.90
Purchase #4	$172.91	10.564%	$191.1762	$191.18	$191.20	$191.20
Purchase #5	$148.60	4.643%	$155.4995	$155.50	$155.50	$155.50
Purchase #6	$111.35	11.236%	$123.8613	$123.86	$123.85	$123.90
Purchase #7	$29.74	9.390%	$32.5326	$32.53	$32.55	$32.50
7 purchase totals =	$723.42		$780.1784	$780.18	$780.20	$780.20