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	$50.51	5.497%	$53.2865	$53.29	$53.30	$53.30
Purchase #2	$45.90	10.263%	$50.6107	$50.61	$50.60	$50.60
Purchase #3	$215.80	11.430%	$240.4659	$240.47	$240.45	$240.50
Purchase #4	$140.52	9.663%	$154.0984	$154.10	$154.10	$154.10
Purchase #5	$184.76	6.537%	$196.8378	$196.84	$196.85	$196.80
Purchase #6	$44.26	9.755%	$48.5776	$48.58	$48.60	$48.60
Purchase #7	$202.62	10.475%	$223.8444	$223.84	$223.85	$223.80
7 purchase totals =	$884.37		$967.7213	$967.73	$967.75	$967.70