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	$35.87	13.833%	$40.8319	$40.83	$40.85	$40.80
Purchase #2	$134.64	4.315%	$140.4497	$140.45	$140.45	$140.40
Purchase #3	$58.92	11.356%	$65.611	$65.61	$65.60	$65.60
Purchase #4	$89.70	11.114%	$99.6693	$99.67	$99.65	$99.70
Purchase #5	$150.59	13.151%	$170.3941	$170.39	$170.40	$170.40
Purchase #6	$220.79	6.329%	$234.7638	$234.76	$234.75	$234.80
Purchase #7	$85.69	5.778%	$90.6412	$90.64	$90.65	$90.60
7 purchase totals =	$776.20		$842.3610	$842.35	$842.35	$842.30