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	$37.66	5.845%	$39.8612	$39.86	$39.85	$39.90
Purchase #2	$82.55	8.368%	$89.4578	$89.46	$89.45	$89.50
Purchase #3	$209.76	8.502%	$227.5938	$227.59	$227.60	$227.60
Purchase #4	$173.71	7.428%	$186.6132	$186.61	$186.60	$186.60
Purchase #5	$203.91	8.555%	$221.3545	$221.35	$221.35	$221.40
Purchase #6	$221.28	7.754%	$238.4381	$238.44	$238.45	$238.40
Purchase #7	$191.93	7.135%	$205.6242	$205.62	$205.60	$205.60
7 purchase totals =	$1,120.80		$1,208.9428	$1,208.93	$1,208.90	$1,209.00