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	$232.86	7.248%	$249.7377	$249.74	$249.75	$249.70
Purchase #2	$108.90	4.848%	$114.1795	$114.18	$114.20	$114.20
Purchase #3	$119.49	9.828%	$131.2335	$131.23	$131.25	$131.20
Purchase #4	$101.68	4.777%	$106.5373	$106.54	$106.55	$106.50
Purchase #5	$39.79	10.337%	$43.9031	$43.90	$43.90	$43.90
Purchase #6	$78.98	13.561%	$89.6905	$89.69	$89.70	$89.70
Purchase #7	$223.50	7.636%	$240.5665	$240.57	$240.55	$240.60
7 purchase totals =	$905.20		$975.8481	$975.85	$975.90	$975.80