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	$137.90	13.144%	$156.0256	$156.03	$156.05	$156.00
Purchase #2	$250.61	6.199%	$266.1453	$266.15	$266.15	$266.10
Purchase #3	$117.34	8.459%	$127.2658	$127.27	$127.25	$127.30
Purchase #4	$5.31	5.316%	$5.5923	$5.59	$5.60	$5.60
Purchase #5	$116.69	12.328%	$131.0755	$131.08	$131.10	$131.10
Purchase #6	$248.81	11.721%	$277.973	$277.97	$277.95	$278.00
Purchase #7	$133.97	8.839%	$145.8116	$145.81	$145.80	$145.80
7 purchase totals =	$1,010.63		$1,109.8891	$1,109.90	$1,109.90	$1,109.90