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	$33.75	13.406%	$38.2745	$38.27	$38.25	$38.30
Purchase #2	$40.86	3.754%	$42.3939	$42.39	$42.40	$42.40
Purchase #3	$98.59	4.258%	$102.788	$102.79	$102.80	$102.80
Purchase #4	$66.58	11.491%	$74.2307	$74.23	$74.25	$74.20
Purchase #5	$14.69	5.334%	$15.4736	$15.47	$15.45	$15.50
Purchase #6	$35.26	9.258%	$38.5244	$38.52	$38.50	$38.50
Purchase #7	$118.25	4.600%	$123.6895	$123.69	$123.70	$123.70
7 purchase totals =	$407.98		$435.3746	$435.36	$435.35	$435.40