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	$147.71	5.534%	$155.8843	$155.88	$155.90	$155.90
Purchase #2	$24.52	4.409%	$25.6011	$25.60	$25.60	$25.60
Purchase #3	$55.72	9.476%	$61	$61.00	$61.00	$61.00
Purchase #4	$31.91	10.397%	$35.2277	$35.23	$35.25	$35.20
Purchase #5	$25.75	8.176%	$27.8553	$27.86	$27.85	$27.90
Purchase #6	$217.80	8.109%	$235.4614	$235.46	$235.45	$235.50
Purchase #7	$17.32	8.670%	$18.8216	$18.82	$18.80	$18.80
7 purchase totals =	$520.73		$559.8514	$559.85	$559.85	$559.90