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	$67.54	12.232%	$75.8015	$75.80	$75.80	$75.80
Purchase #2	$80.85	9.225%	$88.3084	$88.31	$88.30	$88.30
Purchase #3	$158.28	4.313%	$165.1066	$165.11	$165.10	$165.10
Purchase #4	$211.40	10.348%	$233.2757	$233.28	$233.30	$233.30
Purchase #5	$81.89	4.803%	$85.8232	$85.82	$85.80	$85.80
Purchase #6	$50.31	10.216%	$55.4497	$55.45	$55.45	$55.40
Purchase #7	$106.47	7.870%	$114.8492	$114.85	$114.85	$114.80
7 purchase totals =	$756.74		$818.6143	$818.62	$818.60	$818.50