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	$82.90	8.691%	$90.1048	$90.10	$90.10	$90.10
Purchase #2	$109.35	6.602%	$116.5693	$116.57	$116.55	$116.60
Purchase #3	$59.95	3.714%	$62.1765	$62.18	$62.20	$62.20
Purchase #4	$52.99	11.563%	$59.1172	$59.12	$59.10	$59.10
Purchase #5	$230.85	9.688%	$253.2147	$253.21	$253.20	$253.20
Purchase #6	$32.70	12.212%	$36.6933	$36.69	$36.70	$36.70
Purchase #7	$151.92	10.587%	$168.0038	$168.00	$168.00	$168.00
7 purchase totals =	$720.66		$785.8796	$785.87	$785.85	$785.90