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	$240.98	13.158%	$272.6881	$272.69	$272.70	$272.70
Purchase #2	$82.73	8.744%	$89.9639	$89.96	$89.95	$90.00
Purchase #3	$62.35	6.820%	$66.6023	$66.60	$66.60	$66.60
Purchase #4	$198.73	10.441%	$219.4794	$219.48	$219.50	$219.50
Purchase #5	$248.98	7.658%	$268.0469	$268.05	$268.05	$268.00
Purchase #6	$193.94	5.715%	$205.0237	$205.02	$205.00	$205.00
Purchase #7	$95.43	6.790%	$101.9097	$101.91	$101.90	$101.90
7 purchase totals =	$1,123.14		$1,223.7140	$1,223.71	$1,223.70	$1,223.70