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	$84.38	7.199%	$90.4545	$90.45	$90.45	$90.50
Purchase #2	$57.59	8.535%	$62.5053	$62.51	$62.50	$62.50
Purchase #3	$184.34	11.322%	$205.211	$205.21	$205.20	$205.20
Purchase #4	$214.81	3.224%	$221.7355	$221.74	$221.75	$221.70
Purchase #5	$235.77	9.261%	$257.6047	$257.60	$257.60	$257.60
Purchase #6	$105.36	3.349%	$108.8885	$108.89	$108.90	$108.90
Purchase #7	$88.77	13.612%	$100.8534	$100.85	$100.85	$100.90
7 purchase totals =	$971.02		$1,047.2529	$1,047.25	$1,047.25	$1,047.30