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	$81.70	11.582%	$91.1625	$91.16	$91.15	$91.20
Purchase #2	$48.43	9.217%	$52.8938	$52.89	$52.90	$52.90
Purchase #3	$168.32	8.771%	$183.0833	$183.08	$183.10	$183.10
Purchase #4	$82.81	3.724%	$85.8938	$85.89	$85.90	$85.90
Purchase #5	$8.55	12.438%	$9.6134	$9.61	$9.60	$9.60
Purchase #6	$164.90	6.496%	$175.6119	$175.61	$175.60	$175.60
Purchase #7	$79.83	13.494%	$90.6023	$90.60	$90.60	$90.60
7 purchase totals =	$634.54		$688.8610	$688.84	$688.85	$688.90