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	$28.61	9.433%	$31.3088	$31.31	$31.30	$31.30
Purchase #2	$116.57	9.271%	$127.3772	$127.38	$127.40	$127.40
Purchase #3	$155.53	12.853%	$175.5203	$175.52	$175.50	$175.50
Purchase #4	$76.68	12.852%	$86.5349	$86.53	$86.55	$86.50
Purchase #5	$35.28	5.861%	$37.3478	$37.35	$37.35	$37.30
Purchase #6	$171.25	12.722%	$193.0364	$193.04	$193.05	$193.00
Purchase #7	$228.47	9.429%	$250.0124	$250.01	$250.00	$250.00
7 purchase totals =	$812.39		$901.1378	$901.14	$901.15	$901.00