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	$81.48	10.309%	$89.8798	$89.88	$89.90	$89.90
Purchase #2	$231.70	9.425%	$253.5377	$253.54	$253.55	$253.50
Purchase #3	$84.47	11.291%	$94.0075	$94.01	$94.00	$94.00
Purchase #4	$150.60	5.815%	$159.3574	$159.36	$159.35	$159.40
Purchase #5	$104.41	6.446%	$111.1403	$111.14	$111.15	$111.10
Purchase #6	$120.26	10.732%	$133.1663	$133.17	$133.15	$133.20
Purchase #7	$230.25	10.325%	$254.0233	$254.02	$254.00	$254.00
7 purchase totals =	$1,003.17		$1,095.1123	$1,095.12	$1,095.10	$1,095.10