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	$232.94	10.406%	$257.1797	$257.18	$257.20	$257.20
Purchase #2	$208.32	3.256%	$215.1029	$215.10	$215.10	$215.10
Purchase #3	$237.28	9.445%	$259.6911	$259.69	$259.70	$259.70
Purchase #4	$225.57	3.677%	$233.8642	$233.86	$233.85	$233.90
Purchase #5	$89.72	9.667%	$98.3932	$98.39	$98.40	$98.40
Purchase #6	$40.77	10.732%	$45.1454	$45.15	$45.15	$45.10
Purchase #7	$130.43	7.702%	$140.4757	$140.48	$140.50	$140.50
7 purchase totals =	$1,165.03		$1,249.8522	$1,249.85	$1,249.90	$1,249.90