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	$29.37	7.155%	$31.4714	$31.47	$31.45	$31.50
Purchase #2	$49.96	3.597%	$51.7571	$51.76	$51.75	$51.80
Purchase #3	$35.45	5.131%	$37.2689	$37.27	$37.25	$37.30
Purchase #4	$167.29	6.260%	$177.7624	$177.76	$177.75	$177.80
Purchase #5	$39.27	9.848%	$43.1373	$43.14	$43.15	$43.10
Purchase #6	$27.96	13.695%	$31.7891	$31.79	$31.80	$31.80
Purchase #7	$117.66	11.202%	$130.8403	$130.84	$130.85	$130.80
7 purchase totals =	$466.96		$504.0265	$504.03	$504.00	$504.10