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	$237.43	4.695%	$248.5773	$248.58	$248.60	$248.60
Purchase #2	$168.43	10.374%	$185.9029	$185.90	$185.90	$185.90
Purchase #3	$143.61	8.709%	$156.117	$156.12	$156.10	$156.10
Purchase #4	$144.90	8.619%	$157.3889	$157.39	$157.40	$157.40
Purchase #5	$241.64	7.526%	$259.8258	$259.83	$259.85	$259.80
Purchase #6	$17.73	6.624%	$18.9044	$18.90	$18.90	$18.90
Purchase #7	$245.51	7.485%	$263.8864	$263.89	$263.90	$263.90
7 purchase totals =	$1,199.25		$1,290.6027	$1,290.61	$1,290.65	$1,290.60