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	$228.98	11.764%	$255.9172	$255.92	$255.90	$255.90
Purchase #2	$112.56	12.755%	$126.917	$126.92	$126.90	$126.90
Purchase #3	$39.48	6.747%	$42.1437	$42.14	$42.15	$42.10
Purchase #4	$137.27	4.360%	$143.255	$143.26	$143.25	$143.30
Purchase #5	$111.39	4.407%	$116.299	$116.30	$116.30	$116.30
Purchase #6	$234.72	11.663%	$262.0954	$262.10	$262.10	$262.10
Purchase #7	$11.47	3.541%	$11.8762	$11.88	$11.90	$11.90
7 purchase totals =	$875.87		$958.5035	$958.52	$958.50	$958.50