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	$116.25	5.181%	$122.2729	$122.27	$122.25	$122.30
Purchase #2	$175.40	12.635%	$197.5618	$197.56	$197.55	$197.60
Purchase #3	$189.57	7.592%	$203.9622	$203.96	$203.95	$204.00
Purchase #4	$152.65	7.765%	$164.5033	$164.50	$164.50	$164.50
Purchase #5	$145.54	13.247%	$164.8197	$164.82	$164.80	$164.80
Purchase #6	$34.51	3.254%	$35.633	$35.63	$35.65	$35.60
Purchase #7	$105.47	5.320%	$111.081	$111.08	$111.10	$111.10
7 purchase totals =	$919.39		$999.8339	$999.82	$999.80	$999.90