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	$228.77	4.131%	$238.2205	$238.22	$238.20	$238.20
Purchase #2	$134.25	6.755%	$143.3186	$143.32	$143.30	$143.30
Purchase #3	$188.90	10.577%	$208.88	$208.88	$208.90	$208.90
Purchase #4	$241.47	12.628%	$271.9628	$271.96	$271.95	$272.00
Purchase #5	$12.33	12.589%	$13.8822	$13.88	$13.90	$13.90
Purchase #6	$53.34	10.162%	$58.7604	$58.76	$58.75	$58.80
Purchase #7	$51.84	13.803%	$58.9955	$59.00	$59.00	$59.00
7 purchase totals =	$910.90		$994.0200	$994.02	$994.00	$994.10