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	$250.83	8.194%	$271.383	$271.38	$271.40	$271.40
Purchase #2	$233.45	3.393%	$241.371	$241.37	$241.35	$241.40
Purchase #3	$246.65	5.349%	$259.8433	$259.84	$259.85	$259.80
Purchase #4	$41.33	10.565%	$45.6965	$45.70	$45.70	$45.70
Purchase #5	$250.43	5.192%	$263.4323	$263.43	$263.45	$263.40
Purchase #6	$197.35	10.671%	$218.4092	$218.41	$218.40	$218.40
Purchase #7	$84.27	4.817%	$88.3293	$88.33	$88.35	$88.30
7 purchase totals =	$1,304.31		$1,388.4646	$1,388.46	$1,388.50	$1,388.40